Coal Reactivity Research Articles

Cleaning of Thar coal by froth flotation and water washing

The demand for a constant supply of energy is increasing day by day. To meet these increasing demands the natural resources must be utilized smartly. Coal can be a promising fuel due to its large reserves available in Pakistan. About 175 billion tons of coal reserves are found in Thar region of Sindh province. The major issue is the pre-processing cleaning of coal after it is mined out. A number of methods have been adopted to clean coal.
 Presently, cleaning of Thar coal was carried out using froth flotation and water washing techniques. Three different particle sizes (-60#, -100# and -150#) were employed to study the effect of froth flotation on ash and sulfur reduction. Experiments were carried out in laboratory flotation cell and beakers under different set of conditions (i.e., flotation with and without collector and frother and by simple water washing). Kerosene oil was used as a collector and pine oil as a frother. Characterization of raw and treated Thar coal samples was carried out by ASTM standards. The results exhibited an inverse relationship of particle size towards efficiency of the cleaning process; thus, the optimal combustible recovery was attained at -150# particle size. Furthermore, FTIR results disclosed the presence of aromatic and aliphatic structure in treated coal samples. Thermo-gravimetric analysis was also made to determine the weight loss in raw and treated samples and observed increased combustion efficiency and reactivity of Coal.

Substantiation of Practical Recommendations on the Organization of Optimal Modes of Preliminary Heat Treatment and Combustion of Coal in a Pulverized State

Based on the data on the reactivity of coal, a calculated justification of the requirements for the organization of its preparation and combustion processes was carried out, taking into account the initial quality and operating modes of the preparation systems and combustion devices of power steam boilers. The relationship between such operating parameters of the device for preliminary heat treatment of coal as the size of pulverized coal particles, temperature and duration of treatment with the quality of the source fuel has been established in order to ensure stable ignition and completeness of burnout of the products of thermochemical transformation of coal in the conditions of the furnace chamber of the boiler unit. The results of the cycle of analytical studies are summarized and brought to the level of engineering methodology (in the form of a nomogram), which allows determining the optimal values of temperature and time of the process of preliminary heat treatment of coal before combustion in the furnace chamber of a steam boiler based on the known characteristics of the initial fuel (reactivity and particle size). The found operating parameters of the device for preliminary heat treatment of coal ensure the performance of verification (thermal) and design calculations of real fuel-using installations, for example, fuel-free kindling and dust preparation systems. It is established that the most optimal mode of preliminary heat treatment of brown Kansk-Achinsk coals polyfraction, in terms of the efficiency of ignition and combustion of heat treatment products, is 800–850°C with a processing time of 0.6–1.2 s. The results of the calculated studies were confirmed during experimental work on a special laboratory stand, which provides a mode of preliminary heat treatment of coal in a pulverized state in a wide temperature range and afterburning of dust and gaseous heat treatment products under various conditions.

Construction and verification of vitrinite-rich and inertinite-rich Zhundong coal models at the aggregate level: new insights from the spatial arrangement and thermal behavior perspective.

To explore the thermal behavior of Zhundong coal from the perspective of maceral, it is essential to conduct molecular simulations based on constructing a realistic aggregate model of coal. Here, two Zhundong coal samples ZD-V (vitrinite-rich) and ZD-I (inertinite-rich) were collected, and coal models were constructed using elemental analysis, solid-state 13C-nuclear magnetic resonance (13C-NMR), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectrometry (FTIR). The chemical formulas of 2D vitrinite-rich coal and inertinite-rich coal constructed are C152H167NO36 and C155H119NO28, respectively. The chemical structure information matches well with that determined by those analysis results, including elemental analysis, structural composition, and 13C-NMR spectra. The final aggregate models show that the dimension of the unit cell is 2.785 × 2.785 × 2.785 nm for ZD-V and 2.743 × 2.743 × 2.743 nm for ZD-I, including six macromolecules respectively. The final aggregate structure models were verified by comparing experiments and simulation results. In addition to the verification with He density, the spatial arrangement of the aggregate model was verified by simulated XRD spectrum. And moreover, the thermal behavior was verified by ReaxFF MD, and the simulated trend of thermal weight loss and cumulative total molecules released were consistent with TG-MS. The final models show the visual difference between ZD-V and ZD-I, whether the 2D molecular structure or aggregation state. ZD-V is dominated by chain hydrocarbons, while ZD-I is dominated by cyclic hydrocarbons with linked aromatic rings. The aromatic substitution of oxygen atoms is different, ZD-V is mainly composed of ortho-disubstituted arenes, and ZD-I is mainly composed of meta-disubstituted arenes. In addition, ZD-V has a lower ultra-micropore size distribution and porosity than ZD-I. This study presents a comprehensive approach to construct and verify aggregate models from the spatial arrangement and thermal behavior perspective, and the constructed Zhundong coal models can provide a foundation for further exploration of the thermal reactivity (e.g. combustion, liquefaction, etc.) of coal from maceral aspects.

Comparative study on the electrochemical performance of coals and coal chars in a molten carbonate direct carbon fuel cell with a novel anode structure

Molten carbonate direct carbon fuel cells (MC-DCFCs) allow the efficient and clean use of coal. In this study, a novel anode structure is designed, and the performances of six coal-based fuels are investigated in MC-DCFC. The mechanisms of performance differences are investigated, as well as the effect of operating temperature on performance. The results reveal the fuel cell performance in the following order: meagre coal (109.8) ≈ bituminous coal (108.7) > bituminous coal char (98.1) > lignite coal (83.7) > lignite coal char (71.3) > meagre coal char (53.2) in mW cm−2. Coal performs better because of its high carbon content, high volatile content, rich oxygen-containing functional groups, larger specific surface area, stronger thermal reactivity, and other factors. The electrochemical reactivity of coal fuel increased with higher reaction temperatures and varied throughout the temperature ranges. This study implies that using coal fuel to commercialize MC-DCFC could be a realistic alternative.

Towards understanding of internal mechanism of coal reactivity enhancement after thermal decomposition at low temperature

Coal after thermal decomposition has high reactivity and can easily self-heating and self-ignite. The spontaneous combustion problem of thermally decomposed coal has been widely concerned, especially in the unsealing of closed fire area, the magmatic erosion area of coal and the storage of low-rank coal after drying. Related studies mainly explain the phenomenon from the perspective of physical pore and moisture, the effect of the chemical decomposition process on the subsequent spontaneous combustion process of coal is worthy of further study. In this paper, the room temperature oxidation of thermal decomposed coal was first carried out. The physical and chemical parameters of coal before and after the decomposition process were than investigated by modern analytical instruments such as scanning electron microscope (SEM), nitrogen adsorption instrument, X-ray diffraction (XRD), infrared spectrometer (FTIR), X-ray photoelectron spectroscopy (XPS) and Electronic paramagnetic resonance (EPR). Results show that a large number of active sites are generated and accumulated in the thermally decomposed coal, and these sites can rapidly oxidize at room temperature, leading to an increase in coal temperature. Changes in physical structures indicate that thermal damage at high temperatures results in the development of cracks and pores. Variations of chemical structures manifest that the coal decomposition process leads to the decomposition of oxygen-containing functional groups and the increase of active alkyl radicals. It is revealed that the thermal decomposition of oxygen-containing functional groups in coal produces a large number of reactive alkyl radicals, and the oxidation of these radicals is the internal reason for the high reactivity and self-heating of thermally decomposed coal. The development of physical structures such as pores and cracks provide a wider oxygen transport channel for the oxidation of the active sites. This paper is of great significance in revealing the spontaneous combustion mechanism of thermally decomposed coal and helping the development of high-efficiency chemical retardant.

FTIR-based study on the effect of deashing on the molecular structure of Hefeng sub-bituminous coal and its liquefaction residue

ABSTRACT Mineral presents an important effect on the structure and reactivity of coal, and deashing pretreatment is one of the most effective ways to remove mineral from coal. However, deashing pretreatment can change the molecular structure of coal, thus affecting its clean and efficient utilization. To understand the effect of deashing on the molecular structure of Hefeng coal (HF) and its liquefaction residue (LR), HF, LR, Hefeng deashed coal (HFAC), and its liquefaction residue (LRAC) were investigated by Fourier transform infrared spectroscopy (FTIR). Results showed that the deashing treatment could destroy the chemical structure of the coal, while the removal of mineral is not conducive to the liquefaction process of HF. After deashing treatment, the relative content of OH–π hydrogen bonds and self-associated –OH hydrogen bonds declined by 22.40% and 32.10%, respectively. For the aliphatic structure, the content of aliphatic –CH2 changed obviously, among which the asymmetric –CH2 reduced by 12.23%, while the symmetric –CH2 added by 15.27%. For the oxygen-containing functional groups, the carboxyl group increased by 118.95%, and the relative content of C–O group reduced by 49.35%. The 5-substitutions of benzene ring almost disappeared after the deashing process, and the 2-substitutions of benzene ring remarkably increased by 148%, which are predominant in the aromatic structure. After liquefaction, compared to HF, the characteristic peaks ascribed to hydroxyl structure, aliphatic structure, and C=O in LR almost vanished, while the intensity of these peaks in LRAC was stronger than that in LR. The relative content of 5- and 4-substitutions of benzene rings dropped by 33.9%, while the content of 2- and 3-substitutions of benzene rings were increased by 45.47% in LRAC. Structural parameters from functional groups indicated that the length of aliphatic chain was shortened in HFAC and LRAC, and the aromaticity and the condensation degree of aromatic ring were decreased.

Research on Co-Combustion Behaviors of Binary and Ternary Blends of Coal, Walnut Shell, and Biochar by TGA

In this paper, the co-combustion behavior of the walnut shell, biochar, and coal, and the respective binary and ternary blends were investigated by thermogravimetric analysis (TGA) in the oxy-fuel atmosphere (21% O2/79% CO2). The combustion reactivity of coal was similar to biochar but lower than that of the walnut shell. The presence of the walnut shell improved the combustion performance of coal and biochar. The interaction between only biochar and coal was inhibited in the binary blends. The presence of the walnut shell in the ternary blend covered up the inhibition between biochar and coal. The average activation energy of each sample was obtained using the Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) kinetic models. The results of this study provide a reference for the rational utilization of biomass and biochar and the practical improvement of the thermal conversion efficiency of coal.

Gasification of lignite from Polish coal mine to hydrogen-rich gas

The efforts of the world research activities involved in clean coal technologies development focus to a considerable extent on integrated hydrogen and power generation technologies based on coal gasification. As an alternative to combustion processes, gasification offers increased efficiency, lower negative environmental impact as well as wider application range of the main product—synthesis gas—in power generation and chemical syntheses. In order to select the most optimal lignite for the purpose of gasification, it is necessary to determine coal reactivity, the key parameter characterizing how fast the fuel reacts with the gasifying medium and controlling its process ability in thermochemical conversion to energy and/or energy carriers. This paper presents the experimental results of oxygen/steam gasification of lignite coal char in a fixed bed reactor under atmospheric pressure and at the temperature of 700, 800 and 900 °C; the samples come from an open pit lignite mine in the southwest of Poland. The effectiveness of the gasification process was tested in terms of the total gas and hydrogen yields, gas composition, carbon conversion rate and chars reactivity.

Effect of sequential thermal dissolution on the structure and pyrolysis characteristics of Naomaohu lignite

Cyclohexane-insoluble portion (CHISP), ethanol-insoluble portion (EISP) and isopropanol-insoluble portion (IPISP) were obtained by sequential thermal dissolution (STD) from Naomaohu lignite (NL), with cyclohexane (CH), ethanol (E) and isopropanol (IP) as the solvent. The insoluble portions were characterized by Ultimate analysis, Scanning electron microscope (SEM), X-ray photoelectron spectrometer (XPS), Fourier transform infrared spectrometer (FTIR), Thermogravimeter (TG-DTG) and Pyrolysis-chromatography/mass spectrometry (Py-GC/MS). As a result, compared to NL, the gradually increased of C element and decreased of O, N and S in the insoluble portion (ISP) demonstrated that STD is a carbon-rich and heteroatom removal process. The yield of CHISP reached 98.64 % and exhibited smooth surface. The existence of –COO– species in EISP and IPISP indicated that E and IP might be esterified or ester-exchanged with carboxylic acid, while the reduced >CO species illustrated that the nucleophilic oxygen atom in E and IP attacked the carbon atom on the carbonyl group in NL. The comprehensive structural parameter (CSPM) and comprehensive volatile release characteristics index (CVRCI) of NL, CHISP, EISP and IPISP were calculated by FTIR and TG-DTG, respectively. Results showed that STD process improves pyrolysis reactivity, and the CSPM was directly related to CVRCI, presenting a linear relationship (R2=0.952). That is, CSPM can be used as an important parameter to predict the pyrolysis reactivity (CVRCI) of coal. Py-GC/MS showed that, compared to NL, the number of group component was increased in CHISP and decreased in EISP and IPISP during the sequential thermal dissolution process, indicating that there might be non-covalent bond break and formation during the process

Fully resolved direct numerical simulation of single coal particle gasification in supercritical water

Supercritical water gasification is a promising technology in the context of carbon neutrality, since it converts coal into hydrogen and easily-captured CO2. A fully resolved direct numerical simulation of single particle gasification in supercritical water is conducted in this paper in order to investigate process details at particle scale. To handle the shrinking reactive particle, a directional ghost-cell immersed boundary method is used with a general Robin-type boundary condition at the interface. Detailed flow field and interphase heat/mass transfer near the reactive coal particle are revealed and compared with standard non-reactive cases – used for validation. They are found to be significantly affected by the combined effect of the reaction-induced Stefan flow, particle shrinking, species generation or destruction, and reaction heat release. The chemical processes are then studied with special attention on the gas-phase reaction time-scale. This study delivers a detailed understanding of coal particle gasification in supercritical water, and provides a first successful test of efficient numerical methods needed for large-scale supercritical water gasification simulations.

Experimental study of the catalytic effect of iron on low-rank coal gasification

Acid-washing low-rank coal samples were loaded with different content of iron catalyst and then pyrolyzed. FT-IR, Raman spectra, and temperature-programmed experiments were used to investigate the influence of iron on the coal char. The FT-IR results revealed that iron catalyst rises the number of –OH, –CH3, and –CH2 functional groups. The Raman spectra results showed that partial large polyaromatic ring structures transform into small polyaromatic ring structures after the addition of iron. The results of temperature-programmed desorption indicated that the number of surface active sites is increased due to the addition of iron. For low-rank coal char with 3% Fe, the number of active sites increased with the increase of adsorption temperature until 800 °C and then start to decrease. At 750 °C, the adsorption capacity of CO2 increased with the increase of time and reached saturation state after 45 min. The results of the char-steam isothermal gasification experiment suggested that the iron catalyst enhances the gasification reactivity of low-rank coal. It is verified that iron catalysts can improve the gasification reactivity of low-rank coal by increasing the number of surface active sites.

Development of rapid CO2 utilizing microbial ecosystem onto the novel & porous FPUF@nZVI@TAC@ASP hybrid for green coal desulphurization

• Coal desulphurization with high CO 2 consumption by bacteria on a hybrid was studied. • FPUF@nZVI@TAC@ASP offered immobilization platform to grow desulphurization bacteria. • nZVI coating enhanced coal desulphurization by breaking C-S bond & iron recycling. • S (43.3), Fe (20), NH 4 (0.08), NO 3 (0.05), PO 4 (0.01) kg/m 3 /day removal witnessed. • 4500 ppm of CO 2 was consumed to remove 1 kg sulphur, makes this study impactful. Self-capturing carbon dioxide (CO 2 ) from the polluted atmosphere and consuming it into the coal reactor for cheap coal desulphurization is an ideal solution to smog and global warming. Herein, a novel engineered microbial ecosystem was developed over zero-valent iron (nZVI) decorated functional polyurethane (FPUF) biocarrier for coal bio-desulphurization coupled with rapid utilization of CO 2 . FPUF was structured with nZVI for quenching sulphur, iron, and nitrogen species from coal, and present them to TAC/ASP microbes for rapid degradation. Self-assembled and rapid CO 2 utilizing microbial ecosystem (FPUF@nZVI@TAC@ASP) was shortly emerged as rapid coal treatment device as it removed CO 2 (54 kg/m 3 /day), sulphur (43.3 kg/m 3 /day), iron (20 kg/m 3 /day), NH 4 + (0.08 kg/m 3 /day), NO 3 – (0.05 kg/m 3 /day), and PO 4 3- (0.01 kg/m 3 /day). Super-high CO 2 fixation along with high sulphur removal rate (43.3 kg/m 3 /day) also yielded 400 mol/h/g protein. That further provided ample supply of HCO 3 – , S 2 O 3 2- and SO 4 2- species to microbes, which ultimately resulted in highly dense microbial ecosystem (14 g/L/h). Highest coal treatment efficiency (90%) was recorded, at sulphur/CO 2 ratio of 20 and 14-h residence time, which was 30 times better performance than previously reported studies. Practical and commercialized application of developed process (tested in 5-liter coal-reactor), was found very impressive, as treatment of 1 kg coal produced 180 g of sulphur and mitigated 4500 ppm of CO 2. The developed process has potential direct industrial application for coal, crude oil, petroleum, flue gas and natural gas desulphurization. This study opens a new gateway for the investigation and design of more innovative desulphurization and CO 2 mitigation researches.

Influence of Moisture Content of the Reactivity of Coal in Ozone

Influence of Moisture Content of the Reactivity of Coal in Ozone

Evaluation of Synergy Between Lignite and Carbonized Biomass During Co-Combustion

Abstract Synergy often occurs between coal and biomass during co-utilization, and the combustion reactivity and combustion properties of coal are affected mainly due to high volatile matter in biomass. However, it is not clear that a synergistic interaction will be encountered if coal is processed with biochar that contains a limited amount of volatiles due to charring process. In this article, the existence of synergy was questioned based on the thermal analysis data obtained from the co-combustion of several biochars and lignite. The biochars produced at 400 °C from lignocellulosic biomasses such as Fraxinus (FR—ash tree), Populus hybrids (PO—hybrid poplar), and Rhododendron (RH) were blended with Turkish lignite (Adıyaman-Golbasi) to form blends that contain 5–15% biochars. These blends were burned in a thermogravimetric analyzer, and the combustion characteristics of the blends were evaluated, considering the criteria that include the reactivity and combustion performance indices including ignition index, comprehensive combustion index, burnout performance index, combustion stability indices, and rate and intensity index. Also, synergy indices such as synergy indicator, synergy factor, and interaction coefficient were calculated to identify the presence and intensity of synergy. It was concluded that depending on the type of biochar and the addition rate, changes occurred in the combustion properties of the coal, which can sometimes be considered as additive behavior and sometimes as a synergistic interaction. The presence of 5% or 10% PO biochar in the blends resulted in very obvious synergies in combustion characteristics according to all eight criteria considered.

Facemasks and ferrous metallurgy: improving gasification reactivity of low-volatile coals using waste COVID-19 facemasks for ironmaking application

The global pandemic response to COVID-19 has led to the generation of huge volumes of unrecyclable plastic waste from single use disposable face coverings. Rotary hearth furnaces can be used to recover Zn and Fe from non-recyclable steelmaking by-product dusts, and waste plastic material such as facemasks could be utilized as a supplementary reductant for the rotary hearth furnace (RHF), but their fibrous form makes milling and processing to appropriate sizing for RHF application extremely challenging. A scalable method of grinding facemasks to powder by melting and mixing with Welsh coal dust reported herein provides a solution to both environmental challenges. The melt-blended PPE/coal dust shows a dramatically improved CO2 gasification reactivity (Ea = 133–159 kJmol−1) when compared to the untreated coal (Ea = 183–246 kJmol−1), because of improved pore development in the coal during the pyrolysis stage of heating and the catalytic activity of the CaO based ash present in the facemask plastic. The results are promising for the application of waste facemasks in recycling steelmaking by-product dusts in rotary hearth furnaces and may also be suitable for direct injection to the blast furnace subject to further study.

CO2 Gasification Reactivity and Syngas Production of Greek Lignite Coal and Ex-Situ Produced Chars under Non-Isothermal and Isothermal Conditions: Structure-Performance Relationships

The presented work explores the structural properties, gasification reactivity, and syngas production of Greek lignite fuel (LG) and ex-situ produced chars during CO2 gasification. Three different slow pyrolysis protocols were employed for char production involving torrefaction at 300 °C (LG300), mild-carbonization at 500 °C (LG500), and carbonization at 800 °C (LG800). Physicochemical characterization studies, including proximate and ultimate analysis, X-ray Diffraction (XRD), and Raman spectroscopy, revealed that the thermal treatment under inert atmospheres leads to chars with increased fixed carbon content and less ordered surface structures. The CO2 gasification reactivity of pristine LG and as-produced chars was examined by thermogravimetric (TG) analysis and in batch mode gasification tests under both isothermal and non-isothermal conditions. The key parameters affecting the devolatilization and gasification steps in the overall process toward CO-rich gas mixtures were thoroughly explored. The gasification performance of the examined fuels in terms of carbon conversion, instant CO production rate, and syngas generation revealed an opposite reactivity order during each stage. TG analysis demonstrated that raw lignite (LG) was more reactive during the thermal devolatilization phase at low and intermediate temperatures (da/dtmax,devol. = 0.022 min−1). By contrast, LG800 exhibited superior gasification reactivity at high temperatures (da/dtmax,gas. = 0.1 min−1). The latter is additionally corroborated by the enhanced CO formation of LG800 samples under both non-isothermal (5.2 mmol) and isothermal (28 mmol) conditions, compared to 4.1 mmol and 13.8 mmol over the LG sample, respectively. The pronounced CO2 gasification performance of LG800 was attributed to its higher fixed carbon content and disordered surface structure compared to LG, LG300, and LG500 samples.

TGA-DSC Combined Coal Analysis as a Tool for QC (Quality Control) and Reactivity Patterns of Coals.

Coal is at present a major fuel source for power generation worldwide and will remain as such in the near future. The most important property of coal that determines its price is its calorific value. However, volatiles, ash, and moisture content are also very important properties needed for the quality control (QC) of the coal used to maintain an optimal operation of coal combustion in a boiler. The determination of these properties is carried out via well-established ASTM/DIN methods, which are slow and time-consuming. This study uses combined thermogravimetric analysis (TGA)/differential thermal calorimetry (DSC) instrumentation as a tool to evaluate the reactivity patterns of the aliphatic versus aromatic content of coals, which is correlated to the volatile content of coals. Two coals, bituminous (American Baily Pittsburgh No. 6) used in Israeli utilities and lignite (brown coal Hambach) used in German power plants, have been investigated in this study. The results show that the combined TG/DSC method can provide a much better understanding of the chemical reactivity of coals in the combustion process.

Deactivation of Honeycomb Ceramic Metal Catalysts after Stability Tests in an Industrial Coal Combustion Reactor

Deactivation of Honeycomb Ceramic Metal Catalysts after Stability Tests in an Industrial Coal Combustion Reactor

Gasification and structural behaviour of different carbon sources and resultant chars from rapid devolatilization for HIsarna alternative ironmaking process

To evaluate the potential of using renewable biomass in the novel HIsarna technology, reactivity of thermal coal (TC), charcoal (CC), Bana grass char (BGC) before and after rapid devolatilization at 1500 °C in a drop tube furnace (DTF) was investigated. Thermogravimetric (TG) was used for CO2 gasification study, and high temperature confocal scanning laser microscope (HT-CSLM), Brunauer-Emmett-Teller (BET) and scanning electron microscopy (SEM) were used to characterise the morphology of all three raw carbonaceous materials and their chars produced by rapid devolatilization. CC has fastest gasification reaction before and after rapid heat treatment, and BGC raw is more reactive than TC raw but BGC 1500 °C and TC 1500 °C have very similar gasification behaviour. The reactivity index of the rapidly devolatilized char is reduced to 84.21% (BGC), 92.11% (TC) and 94.23% (CC) compared to their raw materials. This shows that BGC is more severely affected by the rapid devolatilization, and this behaviour is likely to be governed by the high ash content which will melt and cause pore blockage during heat treatment. According to HT-CSLM results the average particle sizes decreased by 28%, 24% and 20 % for TC, CC and BGC respectively. While the SEM images shown that TC has gone through significant structural changes during the rapid devolatilization, but CC and BGC maintained their parent structural shapes. The BET results indicate that TC is non-porous, but both CC and BGC contain a large number of constricted micropores with significantly larger surface area.

Reactivity of Coal with Ozone

Reactivity of Coal with Ozone