Coals Of Different Rank Research Articles

Additivity of pore structural parameters of granular activated carbons derived from different coals and their blends

A series of granular activated carbons (GACs) were prepared by briquetting method from Chinese coals of different ranks and their blends, with coal pitch as the binder. Pore structural parameters including BET specific surface area (SBET), total pore volume (VT) and average pore diameter (da) were measured and calculated as well as process parameters such as yield of char (CY) and burn-off (B). The relationship between the pore structural parameters of the GAC from coal blend (BC-GAC) and the ones of the GACs from corresponding single coals (SC-GACs) was analyzed, in which an index, the relative error (δ), was presented to define the bias between fitted values and experimental values of these parameters of the BC-GACs. The results show that the BC-GAC keeps qualitatively the pore structural features of the SC-GACs; as concerned as the quantitative relationship, the pore structural parameters of the BC-GAC from coal blend consisting of non-caking coals can be obtained by adding proportionally the pore structural parameters of the SC-GACs with δ less than 10%. Meanwhile, for the BC-GAC from coal blend containing weak caking bituminous coal, the δ increases up to 25% and the experimental pore size distribution differs greatly from the fitted one.

The influence of ibuprofen ((RS)-2-[4-(2-methylpropyl)phenyl]propanoic acid) additive on the structure ordering of coals of different rank during the process of co-pyrolysis

ABSTRACTThe mechanism of influence of the addition of 2 wt% of the expired pharmaceuticals (EPs) containing 80% of ibuprofen ((RS)-2-[4-(2-methylpropyl)phenyl]propanoic acid) on the transformation of the ordered structure of the three coals of different ranks was studied. The co-pyrolysates of coals with EP additive were studied with the method of X-ray diffraction (ХRD) and scanning electron microscopy (SEM). It was stated that the addition of 2 wt% of EP to all coals under study increases the intra-crystalline ordering. Under the influence of the addition of 2 wt% of EP at the stage of swollen grains of the co-pyrolysates of all coals, the amount of carbon ordered in crystallites decreases. In the co-pyrolysates of lower-rank coals (LRC) and higher-rank coals (HRC) under the influence of this additive at the stage of coke, the amount of the ordered phase decreases compared to the pyrolysates. In the co-pyrolysate of a medium-rank coal (MRC), the degree of ordering of coke does not change compared to the coke from single coal.

Research on the Composition and Distribution of Organic Sulfur in Coal.

The structure and distribution of organic sulfur in coals of different rank and different sulfur content were studied by combining mild organic solvent extraction with XPS technology. The XPS results have shown that the distribution of organic sulfur in coal is related to the degree of metamorphism of coal. Namely, thiophenic sulfur content is reduced with decreasing metamorphic degree; sulfonic acid content rises with decreasing metamorphic degree; the contents of sulfate sulfur, sulfoxide and sulfone are rarely related with metamorphic degree. The solvent extraction and GC/MS test results have also shown that the composition and structure of free and soluble organic sulfur small molecules in coal is closely related to the metamorphic degree of coal. The free organic sulfur small molecules in coal of low metamorphic degree are mainly composed of aliphatic sulfides, while those in coal of medium and high metamorphic degree are mainly composed of thiophenes. Besides, the degree of aromatization of organic sulfur small molecules rises with increasing degree of coalification.

Thermal behavior and microcharacterization analysis of second-oxidized coal

Among coal-producing countries, China has witnessed the highest frequency and severity of coal fires. During mining in the re-mining face and the lower part of the thick coal seam (or coal seam group), second or multiple oxidations of the residual coal can readily occur in mined-out areas, severely increasing the risk of coal fires. The study of multiple oxidations of coal aids in the early detection of spontaneous combustion of remaining coal in the mined-out areas. The characteristics of coal fires are demonstrated using fresh coal samples (first-oxidized coal) and oxidized coal samples (second-oxidized coal) from four different ranks of coals. Proximate and elemental analysis, Fourier transform spectroscopy, and thermogravimetry–differential scanning calorimetry were adopted to investigate the quality, microcharacteristics, characteristic temperatures, and apparent activation energy of second-oxidized coal. In addition, the effect of spontaneous combustion at heating rates of 5.0, 10.0, and 15.0 °C min−1 was studied. Compared with the four samples of first-oxidized coal, those of second-oxidized coals cause fire easily under the same conditions.

Genetic programming based high performing correlations for prediction of higher heating value of coals of different ranks and from diverse geographies

The higher heating value (HHV) is the most important indicator of a coal's potential energy yield. It is commonly used in the efficiency and optimal design calculations pertaining to the coal combustion and gasification processes. Since the experimental determination of coal's HHV is tedious and time-consuming, a number of proximate and/or ultimate analyses based correlations—which are mostly linear—have been proposed for its estimation. Owing to the fact that relationships between some of the constituents of the proximate/ultimate analyses and the HHV are nonlinear, the linear models make suboptimal predictions. Also, a majority of the currently available HHV models are restricted to the coals of specific ranks or particular geographical regions. Accordingly, in this study three proximate and ultimate analysis based nonlinear correlations have been developed for the prediction of HHV of coals by utilizing the computational intelligence (CI) based genetic programming (GP) formalism. Each of these correlations possesses following noteworthy characteristics: (i) the highest HHV prediction accuracy and generalization capability as compared to the existing models, (ii) wider applicability for coals of different ranks and from diverse geographies, and (iii) structurally lower complex than the other CI-based existing HHV models. It may also be noted that in this study, the GP technique has been used for the first time for developing coal-specific HHV models. Owing to the stated attractive features, the GP-based models proposed here possess a significant potential to replace the existing models for predicting the HHV of coals.

Effect of the acid–base composition of water on the wettability of coals of different ranks (Short Communication)

The results of the experimental studies allowed us to assume that the process characteristics determined by the wettability of coal (dust suppression, hydraulic fracturing, coal washing, etc.) may be insensitive to the acid–base composition of utilized water in a range of pH 4.6–10.

Fluidized bed co-combustion of hydrothermally treated paper sludge with two coals of different rank

Fluidized bed co-combustion of raw paper sludge (Raw-PS) and hydrothermally treated paper sludge (HTT-PS) with either low (Lo-Coal) or high reactivity coal (Hi-Coal) was investigated. The paper sludge was treated in a pilot-scale hydrothermal reactor at 197°C and 1.9MPa for 30min. South African bituminous and Thai subbituminous coals were selected as representative of Lo-Coal and Hi-Coal, respectively. A 110-mm bubbling fluidized bed combustor was used in this study. During the steady combustion tests the nominal temperature was 858°C, the fluidization velocity was 0.5m/s, and the excess air was varied as 20%, 40%, and 60%. Both single fuel combustion and co-combustion were tested. Co-combustion tests were conducted by feeding the sludge at mixing ratios of 30% and 50% (mass basis) with coal. The main focus of this study was on NOx emissions and unburned carbon performance. Results showed that at 30% mixing ratio using HTT-PS instead of Raw-PS could reduce NOx emission by 3–6% and 9–17% in the case of Lo-Coal and Hi-Coal, respectively, and the loss of unburned carbon could be decreased by 15–18% and 36–53% for Lo-Coal and Hi-Coal, respectively. The particle size distribution of fly ash of all samples was similar regardless of the excess air variation. On the whole, the hydrothermally treated paper sludge showed better performance for co-combustion with coal and would be a better choice compared to the original raw paper sludge.

Reduction of Sulfur Dioxide Emissions by Burning Coal Blends

Given that sulfur contents of coals vary widely, this work investigated whether cofiring of high-sulfur coals with low-sulfur coals of different ranks has any distinct advantages on lowering the sulfur dioxide emissions of the former coals, beyond those predicted based on their blending proportions. Such cofiring intends to take advantage of documented evidence in previous investigations at the author's laboratory, which demonstrated that lignite coals of low-sulfur, high-calcium, and high-sodium content undergo massive bulk fragmentation during their devolatilization. This particular behavior generates a large number of small-sized char particles which, upon effective dispersion in the gas, can heterogeneously absorb the emitted sulfur dioxide gases, i.e., act as defacto sorbents, and then retain them in the ash. This study included two high- and medium-sulfur bituminous coals, two low-sulfur lignite coals, and a sub-bituminous coal. Results showed that bituminous coals burning under substoichiometric (fuel-lean) conditions release most of their sulfur content in the form of SO2 gases, whereas low-ranked coals only partly release their sulfur as SO2. Furthermore, the SO2 emission from coal blends is nonlinear with blend proportions, hence, beneficial synergisms that result in substantial overall reductions of SO2 can be attained. Finally, NOx emissions from coal blends did not show consistent beneficial synergisms under the implemented fuel-lean combustion conditions.

Spectroscopic Elucidation of the Links between Char Morphology and Chemical Structure of Coals of Different Ranks

In this investigation, SAXS and XRD were used to investigate both the physical and chemical changes in six coals of different ranks subjected to heat treatment. The specific surface area which gives an indication of the reactivity of the coal (measures surface area available for reaction) was determined to be in the range of 70.04 - 260.40 m2/cm3 particle volume for lignite from 450°C - 700°C. The specific surface area was determined to be in the range of 51.58 - 239.00 m2/cm3 particle volume for sub-bituminous; 440.60 - 241.70 m2/cm3 particle volume for light volatile bituminous; 452.71 - 247.73 m2/cm3 particle volume for high volatile bituminous; 349.11 - 347.52 m2/cm3 particle volume for semi-anthracite and 333.60 - 125.34 m2/cm3 particle volume for anthracite respectively. On the other hand, the aromaticity was determined in the range of 0.66 - 0.76 for lignite; 0.67 to 0.80 for sub-bituminous; 0.91 - 0.97 for light volatile bituminous; 0.93 - 0.99 for high volatile bituminous; 0.96 - 1.00 for semi-anthracite and 0.96 to 0.99 for anthracite respectively. The porosity, pore size distribution associated with SAXS and the other crystallite parameters identified with XRD were also determined. Links between the physical and chemical parameters were established.

Insights on the combustion and pyrolysis behavior of three different ranks of coals using reactive molecular dynamics simulation

The process of combustion and pyrolysis of coal can be considered to be convoluted where numerous intermediates are expected to form during the course of the reaction.

Understanding of physicochemical properties and formation mechanisms of fine particular matter generated from Canadian coal combustion

A systematic study on the fine particular matter emissions from coal combustion of four kinds of coals of different ranks (lignite, sub-bituminous, bituminous, coking coal), including three typical Canadian coals and a Chinese coal have been presented. The results show that a tri-modal mass size distribution (coarse, fine and ultrafine mode) was commonly identified, and it was confirmed by size-segregated elemental distributions. The tri-modal distribution is of temperature and coal ranks independence. Coarse particles (Da∼5μm) presented as round-shaped sphere with smooth surface. Both round-shaped particles and irregular-shaped particles were observed in fine particles (Da∼0.5μm). Clusters of nano-particles (Da∼0.05μm) were identified in the ultrafine mode. The concentration of fine particles (Da<1μm) generated from the TECK coal is the highest (about 150mg/Nm3), while fine particles (Da<10μm) generated from Boundary coal (about 580mg/Nm3) is highest among the four coals. Higher volatile content in coals gives priority for enhancing the formation of fine particles. Excluded minerals would mostly fragmented to form ash residual with irregular shapes, while part of them would experience coalescence individually to form round-shaped particles with size larger than 10μm. Included minerals adhered firmly on the surface of char particles contribute greater in the irregular-shaped particles in fine mode, while the shedding included minerals from char particles should take the major responsibility for the round shaped particles in fine mode.

Competitive sorption of CH4, CO2 and H2O on natural coals of different rank

Competitive sorption of CH4 and CO2 from a two-component gas mixture has been studied on three coals of different rank (subbituminous coal, high-volatile bituminous coal and anthracite). On each coal, binary excess sorption isotherms were measured in the dry state and after moisture-equilibration at 53% and 97% relative humidity (RH), to investigate the effect of pre-adsorbed water on the CH4 and CO2 sorption and selectivity at 318K. Excess sorption isotherms were determined using a manometric setup and CH4/CO2 feed gas mixtures containing between 70 and 85% of CH4.The total gas (CH4+CO2) excess sorption capacity is reduced by pre-adsorbed moisture, which is most pronounced for the subbituminous coal. A large decrease in excess sorption capacity was observed for the 53% RH moisture equilibrated samples, whereas only a small further decrease was observed upon moisturization to 97% RH. The anthracite had the highest sorption capacity by far, regardless of the amount of pre-adsorbed water.All measurements show a preferential sorption of CO2 at all three moisture states. The CO2 selectivity over CH4 tends to decrease with increasing maturity and moisture content. The mean CO2 selectivity for the three investigated coals varies between 6 and 9.The extended Langmuir model for adsorption of gas mixtures is shown to be an acceptable first order approximation of the measured competitive sorption isotherm.

A new approach to mercury speciation in solids using a thermal desorption technique

Identification of the chemical form of mercury in coals and during the entire combustion process is essential for successfully controlling mercury emissions. However, the speciation of mercury in coal and, in general, in carbonaceous samples has so far proved elusive because of the limitations of current analytical techniques as a consequence of the detection limits of the equipment or interferences originating from the matrix. In this work a new device based on temperature programmed desorption (HgTPD) has been developed to identify mercury species in carbonaceous materials. The samples studied were coals of different rank obtained from around the world and activated carbons that had previously been used as mercury sorbents in simulated coal combustion atmospheres. The mercury species present in both types of sample were identified without any interference from the matrix. This achievement is extremely important as it will contribute to a better understanding of (i) the behavior of mercury species in coal utilization processes and (ii) the retention mechanisms and subsequent stability of the mercury species captured by carbon sorbents.

Catalytic reforming of toluene using a nickel ion-exchanged coal catalyst

Coal is able to form metal complexes via ion-exchange associated with the carboxyl functional groups. In the work, this ion exchange behavior is utilized to disperse catalytically active metals across a coal support. Coal is composed of mostly aromatic rings that exhibit attractive interaction with toluene, and which can enhance the chance of catalytic contact, combined with metal carboxylates. Nickel ions are exchanged on several coals of different ranks, where only low rank coals (LRCs) achieve the fine metallic dispersion. ICP analysis and TEM pictures confirm that 5–18 wt% of nano-scale nickel metals are all around the LRC matrix as a result of forming metal carboxylates. The nickel catalyst supported on an LRC (Ni/LRC) is applied to the steam reforming of toluene at various conditions (temperature, space velocity, and S/C ratio). It shows relatively high and consistent activity even at 400 °C during 10 h continuous operation, indicating that carbon deposition is expected to be less severe probably because of the metal-coal support interaction that avoids the formation of free NiO.

Influence of charcoal fines on the thermoplastic properties of coking coals and the optical properties of the semicoke

The aim of this work is to investigate the influence of the addition of organic inerts such as charcoal with a well-controlled particle size on the development of fluidity in three coking coals of different rank, maceral composition, and rheological properties. Three size fractions of charcoal, <20, 20–80, and 80–212μm, that can be considered as artificially prepared inertinites were used. The different charcoal fractions were added in amounts of 2, 5, 10, and 15wt.% to selected high-quality coking coals with a Gieseler maximum fluidity (Fmax) of 373 (LF), 541 (MF), and 1891 (HF) ddpm. Increasing the amount of charcoal in the blend led to a progressive inverse exponential reduction in fluidity. This reduction was accompanied by a shortening of the fluid interval due to an increase in the softening temperature. In the case of the finest charcoal fraction, the inhibition of fluidity was even more pronounced. The HF coal with a relatively high fluidity was very sensitive to minimum amounts of charcoal addition, losing nearly half of its fluidity when 5wt.% charcoal was added. A similar reduction in Fmax was also observed for LF, while MF with only a slightly higher fluidity displayed a different trend. From the results it can be seen that the inherent characteristics of a coal are critical factors that affect the extent of the reduction in fluidity caused by the incorporation of charcoal. The differences can be partially attributed to the amount of inertinite present in the parent coal and to the macerals within the inertinite, especially fusinite, semifusinite, and inertodetrinite. In relation to petrographic changes in the matrix of the semicokes, there is a general trend for isotropic material to increase and the size of the anisotropic textures to decrease with the addition of charcoal. Inclusions within the semicoke matrix also change according to the amount and the size of the charcoal added to coal.

Fuel Nitrogen Conversion in Chemical Looping with Oxygen Uncoupling of Coal with a CuO-Based Oxygen Carrier

The interest in chemical looping with oxygen uncoupling (CLOU) of coal as a method for CO2 enrichment has increased drastically during recent years. The objective of this work was to experimentally investigate fuel nitrogen conversion in the CLOU process of coal with a CuO-based oxygen carrier in a batch fluidized-bed unit. Three coals of different rank (anthracite, sub-bituminous, and bituminous) and their corresponding chars were used as fuels. Furthermore, experiments of coal combustion under air-fired conditions were performed to recognize the unique pathway of fuel nitrogen conversion in CLOU. Experimental results indicated that NO was formed in the largest amount of total NOx. For the Shenhua bituminous coal that was used, most of the NO, NO2, and N2O from fuel nitrogen was formed during the devolatilization stage of the coal. However, with Xuzhou sub-bituminous coal or Huaibei anthracite as fuels, a certain portion of NO was derived from char-N. Under the current experimental conditions (temperatur...

Thermal evolution of aliphatic and aromatic moieties of asphaltenes from coals of different rank: possible implication to the molecular architecture of asphaltenes

The compositional and structural changes that coal asphaltenes undergo with increasing thermal maturation were investigated using solid-state 13C NMR and Fourier transform infrared spectroscopy. The results show a gradual increase in the relative proportion of carbon content with a concomitant decrease in the hydrogen, sulphur and oxygen content. The amount of aromatic carbon also increases while the aliphatic carbon decreases with increasing maturity. Ester and carboxylic groups are particularly sensitive to maturation and decrease in relative abundance with increasing maturity while the amount of aromatic carbonyl groups increases. In general, the asphaltenes were observed to evolve towards a more thermally stable structure with increasing amounts of aromatic moieties and relatively lower amounts of aliphatic moieties. The results are in agreement with the ultimate dominance of the island molecular architecture (the Yen–Mullins model) in asphaltenes.

Adsorption isotherms and kinetics of activated carbons produced from coals of different ranks.

Activated carbons (ACs) from six coals, ranging from low-rank lignite brown coal to high-rank stone coal, were utilized as adsorbents to remove basic methylene blue (MB) from an aqueous solution. The surface properties of the obtained ACs were characterized via thermal analysis, N2 isothermal sorption, scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and Boehm titration. As coal rank decreased, an increase in the heterogeneity of the pore structures and abundance of oxygen-containing functional groups increased MB coverage on its surface. The equilibrium data fitted well with the Langmuir model, and adsorption capacity of MB ranged from 51.8 to 344.8 mg g⁻¹. Good correlation coefficients were obtained using the intra-particle diffusion model, indicating that the adsorption of MB onto ACs is diffusion controlled. The values of the effective diffusion coefficient ranged from 0.61 × 10⁻¹⁰ to 7.1 × 10⁻¹⁰ m² s⁻¹, indicating that ACs from lower-rank coals have higher effective diffusivities. Among all the ACs obtained from selected coals, the AC from low-rank lignite brown coal was the most effective in removing MB from an aqueous solution.

Oualitative and quantitative ATR-FTIR analysis and its application to coal char of different ranks

This paper analyzes the coal to char stages of char formation of six coals of different ranks by using Fourier transform infrared coupled with attenuated total reflectance (ATR-FTIR). The chars were obtained by coal pyrolysis carried out at temperature range of 450–700°C. The data obtained shows the pragmatic disappearance of the aliphatic hydrogen content with increasing char formation temperature. Numerical evaluation of the spectra enabled the determination of aromaticity, fa. The aromaticity was found to be between 0.66–0.79 for lignite, 0.75–0.90 for sub-bituminous, 0.84–1.00 for low volatile bituminous, 0.83–1.00 for high volatile bituminous, 0.94–1.00 for semi-anthracite, and 0.97–1.00 for anthracite respectively. With increasing rank of coal samples, spectra exhibit rising aromaticity and enhanced condensation of aromatic rings, whereas the aliphatic chain lengths decrease.

Effect of Temperature on the Molecular Weight Distribution in the Different Ranks of Coal during the On-Line Investigation of Coal Pyrolysis Gas Using Direct Photoionization Mass Spectroscopy

Coal pyrolysis gas from different ranks of coal was monitored on real time basis using photoionization mass spectroscopy. The molecular weight distribution of different products as a function of temperature from various coal ranks studied was observed. It was noted that the release of different classes of compounds like phenols, alkenes, alkylated aromatics and aromatic skeletons was temperature dependent. For all the coal ranks at lower temperatures phenols were the main component, with alkenes and alkylated aromatics at slight higher temperatures and aromatic skeletons were released at the highest temperatures studied.