High Volatile Coal Research Articles

Adsorption simulation of gas released during oxidation of bituminous coal

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

Experimental study of ignition and combustion characteristics assisted by laser-induced plasma during oxy-coal atmosphere by optical emission spectroscopy

This investigation aims to understand the enhancement characteristics of plasma-assisted combustion in oxy-coal combustion. A 1064 nm Nd:YAG laser was added into a laminar flow reactor to produce laser-induced plasmas (LIPs). The high-speed visualization of the coal flame was used to reveal combustion's progress and evolution following laser-induced breakdown. To the best of our knowledge, this is the first time LIP has been applied to the optimization of pulverized coal combustion. The optical emission spectroscopy (OES) demonstrats that LIPs can generate adequate free electrons and ions during combustion. When the laser's pulse interval exceeds 60 ms, the LIP has a beneficial impact on combustion. For the heterogeneous reaction, the thermal effect generated by LIP only improves the intensity of flame radiation by 11–33 %. In contrast, the combination of chemical and thermal effects of plasma can result in significant enhancements of radiation intensity for high-volatile coals, with improvements of 76–203 %. Following laser-induced breakdown, the ignition delay time also decreases from lignite to anthracite, and the flame's peak intensity occurs earlier.

Reduction behavior of iron ore powder by high-volatile coal in thermogravimetric–gas chromatographic and kinetic analysis

Reduction behavior of iron ore powder by high-volatile coal in thermogravimetric–gas chromatographic and kinetic analysis

Experimental research on effects of multi-layer injection of the high-temperature preheated pulverized coal on combustion characteristics and NOx emission

Under the background of carbon peak and carbon neutrality, cleanandefficientutilization ofcoal is imperative in China. As a novel combustion technology, the coal self-preheating combustion technology has broadprospectsforapplication, nevertheless, previous studies have mainly focused on limiting NOx generation by simply applying air staging method in the combustor, which made further NOx reduction difficult to achieve. Combining the advantages of reburning technology, this study firstly realized the multi-layer injection of the high-temperature preheated fuel (PF), and investigated the effects of the reburning fuel fraction (RFF), the location of the reburning fuel injection port (RFL) and the coal type on combustion characteristics and NOx emissions. The results revealed that the generated high-temperature PF could continuously and stably enter the down-fired combustor (DFC) for subsequent combustion. In the intensely reducing atmosphere inside the self-preheating device, the released fuel-N was mainly converted to N2, and the combustion performance of the preheated coal char which could be used as an excellent fuel close to gas reburning effect was greatly modified compared with raw coal. To simultaneously achieve efficient and clean combustion of pulverized coal, the favorable RFF and RFL were 10.62%∼15.48% and 600 mm ∼ 800 mm, respectively, corresponding to the residence time in the primary combustion zone and the reburning zone in the range of 0.91 ∼ 0.99 s and 0.87 ∼ 1.11 s, respectively. What’s more, under the same reburning parameters, Alxa lignite coal had the largest NOx reduction rate (32.15%), with NOx emission of 51.36 mg/m3 (@6%O2), while Jincheng anthracite coal had the lowest NOx reduction rate (5.34%) and the highest NOx emission (149.91 mg/m3, @6%O2), and Shenmu bituminous coal achieved ultra-low NOx emission (45.75 mg/m3, @6%O2) with the NOx reduction rate of 28.05%, suggesting that on the basis of air staging, multi-layer injection of PF had more advantages for clean and efficient combustion of high volatile coal.

The Influence of Coal Tar Pitches on Thermal Behaviour of a High-Volatile Bituminous Polish Coal.

The influence of three coal tar pitches (CTPs), having softening points at 86, 94, and 103 °C, on the thermal behaviour of a defrosted high-volatile coal during co-carbonization and co-pyrolysis was studied. The following research techniques were used: X-raying of the coked charge, TG/FT-IR, ATR and UV spectroscopies, extraction, SEM, STEM, and XRD. It was determined that CTP additives change the structure of the coal plastic layer, the thickness of its zones, and the ordering degree of the structure of semi-cokes to a different extent and independently from their softening points. The softening points of CTPs do not influence the composition and yield of volatile products emitted from blends with pitch as well as the composition, structural-chemical parameters, and topological structure of material extracted from coal blends. It is suggested that such a lack of existence of any correlation between the softening points of CTPs and the degree of their influence on the thermal behaviour of coal was caused by the presence of the atoms of metals (Fe and Zn) in the CTPs. These atoms change the course of the carbonization of the CTPs themselves and their influence on organic substance of coal in blends with CTPs.

The Balance and Optimization Model of Coal Supply in the Flow Representation of Domestic Production and Imports: The Ukrainian Case Study

The successful supply of an economy with coal fuel, for a country that carries out its large-scale extraction and import, is a complex production and logistics problem. Violations of the usual supply scheme in conditions of crises in the energy markets, international conflicts, etc., lead to the problem of simultaneous restructuring of the entire supply scheme. This requires changes in the directions and capacities of domestic production and imports. In this article, the above problem is solved by the economic and mathematical model of production type. The developed model includes subsystems of domestic production and import supply. The results of modeling economy supply with thermal coal for different values of demand are given. The model was used to determine the amounts of coal production for Ukraine with the structure of the coal industry of 2021 and under the condition of anthracite consumers’ transformation to the high volatile coal. Simulations have shown that eliminating the use of anthracite requires the modernization of existing coal mines. Under those conditions, the import of high volatile coal will amount to 3.751 million tons in 2030 and 11.8 million tons in 2035. The amounts of coking coal imports will be 5.46 million tons, 5.151 million tons, and 7.377 million tons in 2025, 2030, and 2035, respectively.

Optical diagnostics on coal ignition and gas-phase combustion in co-firing ammonia with pulverized coal on a two-stage flat flame burner

Gradual substitution of coal with green ammonia is a practical approach for the coal power phasedown at a minimal cost of modification, but the ignition and gas-phase reaction during co-firing NH3 with coal remain largely unclear. In this work, we investigate the co-combustion behaviors of NH3 and a high-volatile coal on a two-stage flat flame burner. Remarkably, the post-flame oxygen mole fraction Xi,O2 of the inner stage can be manipulated to reproduce a proper reducing-to-oxidizing environment that coal particles experience in the practical combustor. We first reveal that, under certain values of Xi,O2 and NH3 co-firing energy ratios ENH3, the reaction intensity (manifested by OH-PLIF signals) in the NH3-coal flame is stronger than burning either pure coal or NH3. This synergetic effect originates from an NH3-combustion-induced enhancement of volatile release. We then propose a characteristic time scale τOH from the OH signals for the initiation of overall reactions in the system. In the case of Xi,O2=0, τOH monotonically increases with ENH3, while for Xi,O2=0.2, the trend transitions to a decreasing one. It can be interpreted by comparing τOH with the characteristic O2 diffusion time, coal particle heating time, and the coal pyrolysis time under different Xi,O2. Furthermore, the coal particle ignition in coal-NH3 flames can no longer be determined by visual images. Instead, we apply CH* chemiluminescence to identify the stages of coal particle ignition and volatile combustion in the NH3-coal flame. While NH3 addition has both positive (elevating temperatures & diluting coal particles) and negative (consuming O2) effects on coal ignition, the combined influence of ENH3 is marginal on coal ignition delay time. On the other hand, the volatile combustion time decreases linearly with ENH3, suggesting a pure effect of reduced coal feed rate.

Individual and combined effect of operating and geometric parameters on combustion behaviour of low and high volatile coals

ABSTRACT Pulverized coal injection technology plays a crucial role in controlling the blast furnace process but increasing the combustion efficiency of coal remains a challenge. Towards this, the manuscript attempts to examine the performance of different coals subjected to different operating and geometric parameters through a validated numerical model. Two coals with different volatile matter have been selected for this study while oxygen enrichment, lance position, and particle size distribution have been varied. Among all parameters, particle fineness has proven to be the major contributor towards improving burnout. The underlying mechanism has been explained in terms of oxygen distribution and particle temperature. In addition, the combined effect of all parameters increases the final conversion by 6% and 10% for high and low volatile coals respectively. Ease of volatile release plays an important role in controlling the overall burnout where a higher release rate for high volatile coal somewhat compensates for the impact of the parameters studied.

THE POTENTIAL OF USING THE EARLY EOCENE-OLIGOCENE COAL’S FORMATION IN TANJUNG BARITO BASIN

Research on the development of coal utilization for Indonesia is very important considering that Indonesia is a country that has large amounts of coal reserves, so it can use its coal not only as a source of energy for power plants but also needs to incentivize coal conversion for increased added value. To analyze the potential of using the early Eocene-Oligocene coal's formation in Tanjung Barito basin. In this study, data sources derived from laboratory test results will be analyzed by descriptive methods with quantitative approaches. The results of this study were obtained through proximate tests on coal samples TIAN-0 1 and TIAN-0 2 total value moisture of 9.1 4% weight as-received basis (arb) and Moisture in the Analysis sample worth 3.67%, value ash content 7.35%, flying substance value 36.11%, tethered carbon value 52.86% with air-dried base (ADB) basis % weight and total sulfur value 0.36% with air-dried base (ADB) % weight. Based on the gross calorific value with an average caloric value of 7353 Kcal/kg, sample coal is classified as high volatile coal A bituminous. The results of testing on the potential of sample coal caking also indicate the potential utilization of Early Eocene-Oligocene coal Tanjung Formation to be used in the metallurgical industry with the results of testing the value of the Free Swelling Index sample showing the swelling ability of the coal with a value of 6 and 2.5 and G indexes 66 and 92.

Emission profiles of volatile organic compounds from various geological maturity coal and its clean coal briquetting in China

Coal is a dominant energy source used in household cooking and warming in rural China. Its combustions generate a large quantity of gaseous and particulate phase's pollutants. In between, the volatile organic compounds (VOCs) is a critical class of chemical that shows strong environmental and health impacts. In this study, the VOC emission characteristics, influencing factors and briquette technology that affected the combustions of different maturity coals were investigated. Emission factors (EFs) of targeted non-methane VOCs (EFNMVOCs) for different coal samples ranged from 233 ± 89.8 to 1690 ± 722 mg/kg. The EFNMVOCs decreased with volatile content (VC). Besides, EFNMVOCs for the briquette coals showed 5.31–51.5% lower than that of the raw coals except the anthracite. Alkanes and alkenes are the two most dominated chemical groups, accounting for >50% of the total NMVOCs emissions. Coefficient of divergence (CD) values showed that a significant difference (>0.6) between the emissions of high-volatile and low-volatile raw coals, representing that the coal content should be sub-classified for either source apportionment or emission profile database development. Correlation analysis reported that VC is the most significant factor that correlated with EFNMVOCs (R = 0.78), while modified combustion efficiency (MCE) negatively correlated (R = −0.78). The calculations of ozone formation potentials (OFP) and secondary organic aerosol potentials (SOAP) deducted that alkenes and aromatics are the top two contributors to the formations of these secondary pollutants. In addition, the briquette technology has been proved to reduce both OFP and SOAP from coal combustions. Our results perceptibly support that the use of low VC coals could efficiently reduce the emissions of VOC and the formations of more environmental and health harm substances, and the application of briquetting technology also has a certain effect especially in bituminous coals. The key findings provide feasible solutions to improve regional air quality regarding residential coal combustion in northwest China.

Determination of ignition temperature and kinetics and thermodynamics analysis of high-volatile coal based on differential derivative thermogravimetry

In order to accurately determine the ignition temperature (Ti) of coal, Coal spontaneous combustion (CSC) process was tested by a simultaneous thermal analyzer. Next, the abrupt change point of the differential derivative thermogravimetric curve (DDTG) of coal after the high adsorption temperature was taken as the Ti of CSC. Besides, variations of kinetics and thermodynamics during the CSC before and after the Ti were calculated. It was found that the mass loss, heat releases and gaseous products of coal changed slowly before the Ti and surged sharply after the Ti. The coal at ignition temperature was in thermodynamic equilibrium with low activity. However, when the temperature was greater than Ti, the aromatic hydrocarbons in coal begin to decompose, resulting in the increased of active sites and the release of volatiles, and the coal enters an irreversible combustion stage. At this time, upward trends were obtained for the apparent activation energy, pre-exponential factor, enthalpy change, and entropy change, while a gradual decrease was observed for the Gibbs free energy change. Moreover, reaction intensity between oxygen and coal would be increased due to increased of active sites in the coal and enhanced of volatiles release under a slower heating rate.

Application of <sup>13</sup>C-NMR Coal Structure Analysis for the Formation of Volatile from High-volatile Coals under High-temperature Pressurized Gasifier Conditions

Application of <sup>13</sup>C-NMR Coal Structure Analysis for the Formation of Volatile from High-volatile Coals under High-temperature Pressurized Gasifier Conditions

Speciation and thermal transformation of sulfur forms in high-sulfur coal and its utilization in coal-blending coking process: A review

The utilization of high-sulfur coal is becoming more urgent due to the excessive utilization of low-sulfur, high-quality coal resources, and sulfur removal from high-sulfur coal is the most important issue. This paper reviews the speciation, forms and distribution of sulfur in coal, the sulfur removal from raw coal, the thermal transformation of sulfur during coal pyrolysis, and the sulfur regulation during coal-blending coking of high organic-sulfur coals. It was suggested that the proper characterization of sulfur in coal cannot be obtained only by either chemical method or instrumental characterization, which raises the need of a combination of current or newly adopted characterization methods. Different from the removal of inorganic sulfur from coal, the organic sulfur can only be partly removed by chemical technologies; and the coal structure and property, particularly high-sulfur coking coals which have caking ability, may be altered and affected by the pretreatment processes. Based on the interactions among the sulfur radicals, sulfur-containing and hydrogen-containing fragments during coal pyrolysis and the reactions with minerals or nascent char, regulating the sulfur transformation behavior in the process of thermal conversion is the most effective way to utilize high organic-sulfur coals in the coke-making industry. An in-situ regulation approach of sulfur transformation during coal-blending coking has been suggested. That is, the high volatile coals with an appropriate releasing temperature range of CH4 overlapping well with that of H2S from high organic-sulfur coals is blended with high organic-sulfur coals, and the C–S/C–C bonds in some sulfur forms are catalytically broken and immediately hydrogenated by the hydrogen-containing radicals generated from high volatile coals. Wherein, the effect of mass transfer on sulfur regulation during the coking process should be considered for the larger-scale coking tests through optimizing the ratios of different coals in the coal blend.

Thermal Processing of High-Volatile Coal

Thermal Processing of High-Volatile Coal

Application of synchrotron ATR-FTIR microspectroscopy for chemical characterization of bituminous coals treated with supercritical CO2

Injection of CO2 into deep coal seams has offered great potential to sequester CO2 and while simultaneously enhancing coalbed methane recovery. Unlike other sequestration options, CO2 sequestration in coal is still infancy and requires fundamental knowledge to understand physical and chemical phenomena that happen after CO2 injection in coal. The injected CO2 exists in supercritical state (ScCO2) under reservoir conditions and has great potential to interact with inorganic and organic matters in coal. One of many questions that still need to be answered is how coal structure changes from a chemical perspective upon CO2 exposure. Synchrotron ATR-FTIR microspectroscopy was used to investigate associated changes of the functional groups of high-volatile and low-volatile bituminous coals, before and after processing with ScCO2 for a period of 1 month. With increasing rank of coal samples, the synchrotron ATR-FTIR spectra showed an increasing aromaticity (i.e. ratio of ν(C–H)aromatic to ν(C–H)aliphatic). After being subjected to ScCO2 treatment, the synchrotron ATR-FTIR spectra revealed an increased degree of aromaticity in high-volatile bituminous coal and low-volatile bituminous coal by 16.7% and 21.1%, respectively, due to the loss of aliphatic C–H functional groups. Most of the literature reported that CO2 tends to physically adsorb onto pore surface of coal without chemical reactions. The results of this study provide an evidence of chemical reactions, i.e. mobilization of alkanes due to the ScCO2 treatment. The breakage of the aliphatic C–H bonds increases the degree of aromaticity in the macromolecular structure after ScCO2 exposure, which is analogous to heating treatment of coal. Such findings further reinforce the concept that the ScCO2 acts as a good solvent and can increase macromolecular mobility of coal when it enters the macromolecular structure.

Calibration and validation of a comprehensive kinetic model of coal conversion in inert, air and oxy-fuel conditions using data from multiple test rigs

This work presents detailed information on pyrolysis and char oxidation for a high-volatile Colombian bituminous coal. The investigation includes experiments at low and high particle heating rates, performed in a thermogravimetric analyzer (TGA), a drop-tube reactor (DTR), a flat-flame burner (FFB) and a fluidized-bed reactor (FBR). The TGA and DTR data were used when developing and calibrating the kinetic model for the conversion of coal in air and oxy-fuel atmospheres, while the FFB and FBR data were used to validate the resulting mechanism. The proposed model is an updated version of the CRECK-S-C model from the Politecnico di Milano (PoliMi), consisting of a fuel characterization step, coupled with a multi-step kinetic mechanism based on reference coals. Both the devolatilization and heterogeneous char reactions are accounted for and interconnected seamlessly. Key reactions were introduced and the existing reactions were calibrated to account for the particularities of this fuel and the effects of the abundant CO2 concentration in the reactors. The importance of successive gas-phase reactions was observed and a gas-phase kinetic model was coupled to properly simulate such conditions. The resulting model is applied to simulate and systematically evaluate the experimental findings, highlighting the model’s features and limitations.

Effect of coal rank, oxygen level and particle size on oxidation reactivity of typical Chinese coals

The changeable and deteriorating coal quality in air staging mode threats the safe and economic operation of the boiler. Non-isothermal TGA experiment was performed with varying heating rates (5, 10, 15 and 20 K/min) on six Chinese coals at 20 % O2 and on the lean coal with varying O2 (5%, 10 %, 20 % and 40 %). Isoconversional method is adopted to determine the activation energy (Eα) and frequency factor (Aα). Influence of particle size at varying oxygen concentration is compared between lean coal and bituminous coal at 20 K/min. The characteristic temperature (T0.1, T0.5 and T0.9) increases as the coal rank increases and oxygen level decreases. The slope of the line (characteristic temperature vs. O2) increases from 1.6 to 3.6 as the conversion increases from 0.1 to 0.9, which means the oxygen diffusion has an increasingly important role as the oxidation proceeds. As O2 decreases, the effect of particle size reduction on combustion improvement of low volatile coal is increasingly significant than that of high volatile coal. The smaller economic fineness of coal particle can be established for low volatile coal in low NOx combustion mode compared with that for high volatile coal.

The Influence of Freezing on the Course of Carbonization and Pyrolysis of a Bituminous High-Volatile Coal

The course of thermal behavior of a fresh bituminous high-volatile coal during carbonization and pyrolysis was compared to that of this coal thawed after storage. The research was carried out using the following techniques: X-raying, thermogravimetry/Fourier transform-infrared spectroscopy (TG/FT-IR), extraction, Diffuse Reflectance Infrared Fourier Transform Spectroscopes (DRIFT), Attenuated Total Reflectance (ATR), and SEM. The increase in range of the viscous-liquid state and a decrease in temperature of its appearance were stated along with the formation of a more compact residue at the re-solidification stagtablee for the thawed coal during its carbonization. There is a fourfold reduction in the charge volume. The leakage of bitumen that contains 87 At % of C atoms from swollen grains and a fourfold increase in the yield of the material extracted from these grains are the proof of a greater plasticization of thawed coal. During the pyrolysis of thawed coal, the yield in volatile products of pyrolysis increases, and the composition of these products changes. The contribution ratio of saturated and unsaturated hydrocarbons, CO2, alcohols, and phenols decreases in the composition of volatile products of thawed coal. It is suggested that the use of freezing during the storage of a freshly mined coal that has a poorer caking ability can improve its plasticization during carbonization.

PARAMETRIC STUDY OF THE NON-PREMIXED COAL COMBUSTION IN FURNACE FOR HEAT TRANSFER AND EMISSION CHARACTERISTICS

Steady-state turbulent non-premixed combustion of pulverized coal has been modeled in the two-dimensional furnace. Pulverized coal of three different types, low volatiles coal, medium volatile coal and high volatile coal, has been considered. The coal is injected through the center of the furnace and air is being supplied with two inlets (top inlet and bottom inlet) at different velocities. Taking advantage of the symmetry, only one half of the domain is considered. Results have been validated with the experimental data for furnace temperature distribution. Effect of variation of parameters such as top air velocity, bottom air velocity, air temperature, furnace wall temperature and mass flow rate of coal are discussed for all three different types of coal. The effect of these various parameters has been discussed upon peak temperature inside the furnace, heat transfer to/from the system to surroundings and emission of gases like compounds of NO, CO and CO2. The analysis has been carried out using Ansys-Fluent software.

Combustion interactions in oxy-fuel firing of coal blends: An experimental and numerical study

Coal blends are commonly used in thermal power plants and oxy-fuel combustion also attracts great concerns recently. However, little has been done on oxy-fuel combustion of coal blends. In this paper, combustion tests are performed in a drop tube furnace for various coal blends under O2/CO2 mixtures, which are also reproduced numerically. Strong combustion interactions between the parent coals in a blend are observed. The ignition of the low-volatile coal is promoted due to the rapid combustion of the volatiles from the high-volatile coal. However, the char burnout of the low-volatile coal is compromised due to the rapid O2 consumption by the large amount of volatiles. The interactions under oxy-fuel conditions are more sensitive to the excess O2, inlet oxidizer temperature and coal particle size. 1) The increase in the excess O2 tends to weaken the combustion interactions, in which both the ignition promotion and burnout inhibition effects on the low-volatile coal become less apparent. 2) The increase in the inlet oxidizer temperature further promotes the ignition of the low-volatile coal whereas weakens the burnout inhibition of the low-volatile coal. 3) The effects of reducing particle size on the combustion interactions are similar to those of increasing inlet oxidizer temperature. Since biomass often contains a high volatile content, the findings may shed light on the synergistic effects in oxy-fuel co-combustion of biomass and coal.