Kinds Of Lignite Research Articles

Synergistic mechanism and radicals interaction of the co-pyrolysis of lignite and PE based on ReaxFF-MD and DFT

Co-pyrolysis is a clean and efficient strategy for utilizing coal and plastics to effectively manage plastic waste while improving valuable chemicals. Since coal and plastic belongs to organic macromolecules, the synergistic mechanism is insufficiently clear. In this paper, a kind of lignite and polyethylene (PE) were selected as representatives to study the synergistic effects of the main products during co-pyrolysis. The synergistic mechanism was elucidated at the microscopic level that radicals such as ·H and CnHm· fragments broken from PE broken combined with the tar fragments produced by lignite cleavage, which produces hydrocarbon products. As the temperature increases, the positive synergistic effect of the major liquid and gaseous products increases in a specific temperature range while weakens with a further increase in temperature. Increase of lignite can produce more oxygenated compounds while more hydrocarbons can be obtained by increasing the percentage of PE. The highest synergistic effect occurs at equal ingredients. The energy barriers of the reaction paths in the individual pyrolysis process were higher than those in the co-pyrolysis process, which indicates that the main products, such as aromatic hydrocarbons as well as ethylene are more easily formed in the co-pyrolysis process, thus a manifestation of positive synergistic effect.

Thermodynamic variation law and influence mechanism of low-temperature oxidation of lignite samples with different moisture contents

Coal spontaneous combustion (CSC) is one of the main disasters that threaten the safe production in coal mines. Moisture, which is the main factor affecting coal oxidation, has a considerable impact on CSC. In this paper, the variation characteristics of TG-DTG and DSC-DDSC curves of two kinds of lignite during low-temperature oxidation were investigated. The following results were obtained: Oxidation-induced heat production (OHP) starts to play a leading role in the temperature range of 50–75 °C; pyrolysis-induced heat absorption (PHA) grows faster than OHP in the temperature range of 70–130 °C; and OHP is dominant in the temperature range of 130–260 °C. Furthermore, for coal samples from Shengli (SL) Coal Mine and Yuanbaoshan (YB) Coal Mine, the initial heat release temperature and the end temperature both conform to the Lorentz function T=T0+2A(B4(M−Mc)2+B2). Thermodynamic parameters reach the maximum under the moisture content of 12%–17% where the CSC is the most likely to occur. In the oxygen adsorption and weight gain stage, the activation energy decreases and gradually stabilizes with the increase in moisture content. In the accelerated oxidation stage, moisture in coal plays a chemical catalytic role in the processes of oxygen chemical adsorption and intermediate complex formation and decomposition. However, excessive moisture cannot accelerate the coal-oxygen composite reaction.

Combustion characteristics and synergistic effects during co-combustion of lignite and lignocellulosic components under oxy-fuel condition

Co-combustion of lignocellulosic biomass and coal has been recognized as a promising route to deliver carbon neutrality. In this study, the combustion characteristics of lignocellulosic biomass main components (cellulose, hemicellulose, and lignin), one kind of lignite, and their mixtures were investigated under air and oxy-fuel conditions, respectively. The combustion reactivity of cellulose and hemicellulose was better than that of lignite, while that of lignin was worse. Under the oxy-fuel condition with the same oxygen mole fraction as air, the combustion of cellulose and hemicellulose was slightly delayed, while a distinct combustion delay was observed for lignin similar to lignite. For the co-combustion, compared to lignite, the combustion reactivity could be improved by blending cellulose and hemicellulose, while it got worse by mixing lignin. Cellulose and hemicellulose had a positive synergistic effect on the release of lignite volatiles, while lignin showed a negative synergy on it. All the lignocellulosic components showed positive synergies with lignite on the char oxidation due to the high structural porosity of lignite char and the advanced oxidation of lignocellulosic char.

Gasification reactivity and kinetic parameters of coal chars for non-isothermal steam gasification

The gasification reactivity and kinetic parameters of coal chars for non-isothermal steam gasification were investigated. One kind of lignite and three kinds of bituminous coals were used as the samples, and their coal ranks follow the ascending order: XB KL > ZJ > GD. Through systematically analyzing factors affecting gasification reactivity, it was ascertained that the gasification reactivity is mostly determined by the carbonaceous structure. The gasification reactivity is inversely proportional to the coal rank, and the higher the coal rank, the lower the gasification reactivity. A new kinetic model was proposed to calculate the kinetic parameters, in which the reaction order was considered as an unknown kinetic parameter. The reaction order n follows the ascending order: XB < KL < ZJ < GD, which are n = 1.00, n = 1.34, n = 1.83, and n = 2.63, respectively. It is proved that the reaction order is proportional to the coal rank, and the higher the coal rank, the higher the reaction order.

Comparison of the Contaminants in the Wastewater Produced in the Ex Situ Underground Ortho- and Meta-Lignite Gasification

This work comprises results of the laboratory tests on formation and potential release of contaminants from underground gasification of lignites. Four large scale and multi-day trials were carried out using ex-situ gasification facilities. Two different kinds of lignite were tested, i.e. Velenje lignite (Slovenia) and Oltenia lignite (Romania). Gasification tests were conducted in the artificial coal seams under two distinct pressure regimes—atmospheric and high pressure regime (35 bar and 10 bar for the Velenje and Oltenia samples respectively). The UCG wastewater samples were periodically collected from the gas purification module to measure the rate of the wastewater and contaminants production at each phase of the experiment and to assess the effect of gasification pressure and lignite physicochemical properties. The group of target contaminants included: phenols, aromatic hydrocarbons, and some non-specific water parameters. The effect of gasification pressure was confirmed, especially for BTEX and phenols and significant drops in the contents of these compounds were observed at elevated pressures. The effect of pressure was more pronounced for the geologically older coal (Velenje), i.e. drop in the average concentrations from 1994 μg/l (atmospheric) to 804 μg/l (35 bar) and from 733 mg/l (atmospheric) to 17 mg/l (35 bar) for BTEX and total phenols, respectively. The differences in the macromolecular structure and ash content of the both coals were found to be the main reason behind the differences in the contents of organic and inorganic species respectively. The study also shown that composition of UCG wastewaters significantly varied over the time of the particular experiments, which reflected changes in the gasification thermodynamic conditions and development of oxidation and pyrolysis zones. During the atmospheric gasification experiments, the values of BTEX for the Velenje lignite dropped from 3434 μg/l to 1364 μg/l and for the Oltenia lignite from 1833 μg/l to 978 μg/l. A similar downward trend in the concentrations of BTEX was observed for the pressurized experiments. For the Velenje trial a drop from 1111.6 μg/l to 211.2 μg/l and for the Oltenia - from 1695 μg/l to 688 μg/l was observed. Concentrations of phenolic compounds during the atmospheric gasification experiments varied significantly during both atmospheric trials and no significant trends were noticed.

Enhancement of low‐temperature lignite pyrolysis by recycled carbocoal for high‐quality tar in fixed‐bed reactor

AbstractLignite could be converted to high value‐added char and tar through a pyrolysis process. To improve the tar yield as well as the quality of tar/char during a low temperature (550 °C) lignite pyrolysis (LT‐LP) process, the influence of mixing inexpensive and accessible recycled carbocoal with three kinds of lignite was investigated in a fixed‐bed reactor. The LT‐LP processes with and without recycled carbocoal were investigated using a TGA and were compared in detail. The results indicated that the addition of the recycled carbocoal into the three lignite optimized the light tar yield from 4.63, 3.33, and 2.09 g/g to 10.50, 6.10, and 5.01 g/g, and improved the gasification reactivity of the chars up to 2.88, 2.58, and 2.88 h−1, respectively. To identify the role of recycled carbocoal during the LT‐LP process, the obtained products, such as tar and char, were characterized by chromatography, thermal gravimetric analyzer, chromatograph‐mass spectrometer, elemental analyzer, Fourier transform infrared spectroscopy, and scanning electron microscope. It was demonstrated that the existence of the recycled carbocoal could impede the self‐polymerization of small molecule hydrogen‐containing (SM‐HC) free radicals and cut down the reactions between SM‐HC and hydroxyl radicals at the weak‐bonds breaking zone (300–450 °C), thereby supplying sufficient free radical stabilizers for the tar intermediates at the molecular skeleton region (450–550 °C). The high‐valued tar and char were obtained. In summary, the employment of recycled carbocoal during the LT‐LP process could not only promote the economic benefit of LT‐LP products but also reduce the cost of lignite value‐added utilization.

Efficiency assessment of underground gasification of ortho- and meta-lignite: High-pressure ex situ experimental simulations

Experimental simulations of underground coal gasification (UCG) using large bulk samples of two different kinds of lignite were conducted in an ex situ laboratory installation. The gasified media applied was oxygen under two distinct pressure regimes: 10 and 35 bars. The main aim of the experiments was to assess the feasibility of gas production from low-grade, high-moisture lignite through in situ gasification. The ortho- and meta-lignites subjected to gasification originated from the Oltenia (Romania) and Velenje (Slovenia) deposits. The average moisture content of the raw lignite feed was 45.64%wt and 31.62%wt, with gross calorific values of 10.64 MJ/kg and 13.62 MJ/kg for the Oltenia and Velenje samples, respectively. Changes in the composition of the process gas, its production rates, rates of oxidant supply and the distribution of temperature in the experimental coal seam were measured over the course of both experiments. The UCG trials, each lasting 72 h, constituted of three stages – Initialization, Gasification and Termination, with stage II being considered as the main part of the experiments. The process gas produced during the stage II had an average calorific value of approximately 3.9 MJ/Nm3 and 5.0 MJ/Nm3 for the Oltenia and the Velenje trials, respectively. The overall gross energy efficiency of the process during the stage II was estimated at 25.0% and 29.9% for the Oltenia and Velenje samples, respectively.The experiments conducted demonstrate that the physico-chemical properties of the feed lignite, as well as the pressure at operating conditions, considerably affect the in-seam gasification process. The gasification of the Oltenia lignite resulted in more stable syngas production in terms its chemical composition but lower calorific value. Gasification in a higher-pressure regime resulted in increased methane and carbon dioxide content in the produced syngas, with lower hydrogen and carbon monoxide content.

Effect of hydrothermal treatment on structure and liquefaction behavior of Baiyinhua coal

Baiyinhua (BYH) coal, a kind of lignite, was hydrothermally treated in an autoclave reactor at 200–350°C for 30min and the liquefaction behavior of the treated samples were investigated. To uncouple the complex behavior of the changes in structural characteristics and functional groups of treated samples, the structural change in BYH coal was investigated by thermogravimetry, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Results reveal that oxygen content and volatile matter in treated sample reduce and carbon content increases. The decrease in atomic ratio of oxygen to carbon and hydrogen to carbon of treated sample indicates the improvement in coalification degree. CO2 and CO account for the overwhelming majority of gaseous products from hydrothermal treatment, which can be attributed to the significantly decrease of carboxyl and carbonyl content. The hydrothermal treatment involves the breakup of some weak bonds within coal structure, and the main structure of BYH coal does not change significantly. A desirable upgraded coal was obtained by hydrothermal treatment of BYH raw coal at 250°C. The liquefaction behavior of coal can be improved by hydrothermal treatment at 250°C, and the oil yield increases from 32.9wt% (dry ash-free basis) of raw coal to 37.8wt% (dry ash-free basis). This work illustrates that hydrothermal treatment is a promising approach for upgrading of low rank coal.

Lignite drying with solar energy: Thermodynamic analysis and case study

ABSTRACTAs a clean, free, and nondepleting source, solar energy has become the focus of increasing attention in the drying industry. A lignite-fired power plant integrated with a solar dryer (LPPS), in which solar energy is used to dry lignite and the predried lignite is used to generate electricity, is analyzed theoretically in this paper. The aim of this study is to evaluate the energy performance of solar drying under different system parameters. Thermodynamic models, with which the second-law efficiency of the LPPS could be maximized, were developed. A reference case with three kinds of lignite as input fuel was analyzed to quantify the system performance. The first-law and second-law efficiencies were obtained. The solar-to-electric conversion efficiency in the LPPS is more than 34%. Therefore, solar drying is a potential technology that should be promoted in lignite-deposited areas. Moreover, the influence of main parameters on the performance of system was analyzed. Dryer efficiency is determined to have significant influence on the solar-to-electric conversion efficiency.

The study on the effect of the substitution of K2CO3 with Ca(OH)2 on kinetics on CO2–lignite coal gasification

Three kinds of lignite were mixed with K2CO3 and Ca(OH)2 and were gasified with CO2 to investigate the effect that the addition of Ca(OH)2 had on the gasification kinetics. K2CO3 and Ca(OH)2 were impregnated and dried, their mixing ratio was varied, and the gasification experiments were conducted over a temperature range from 850 to 950 °C at atmospheric pressure. The modified volumetric reaction model was applied as the gas–solid reaction model to analyze the carbon conversion results and thus obtain the kinetic parameters. The results indicate that the catalytic activity based on carbon conversion followed the order of K2CO3 5 wt% + Ca(OH)2 3 wt% > K2CO3 8 wt% > K2CO3 3 wt% + Ca(OH)2 5 wt% > K2CO3 1 wt% + Ca(OH)2 7 wt%. The reaction rate was also influenced by the type of lignite, with a higher reactivity observed for Adaro lignite. The highest reaction rate constant was of 44.25 min−1 with Adaro lignite and K2CO3 5 wt% + Ca(OH)2 3 wt% at 950 °C. The lowest activation energy of 44.49 kJ/min was calculated for Mongolia lignite with K2CO3 8 wt%. The reaction rate was enhanced by partly substituting K2CO3 with Ca(OH)2, but further substitution resulted in a decrease in the reaction rate compared to that of K2CO3 alone.

Energy and water conservation at lignite-fired power plants using drying and water recovery technologies

Lignite is considered as a competitive energy raw material with high security of supply viewed from a global angle. However, lignite-fired power plants have many shortcomings, including high investment, low energy efficiency and high water use. To address these issues, the drying and water recovery technologies are integrated within lignite-fired power plants. Both air-cooling and wet-cooling units with three kinds of lignite as feeding fuel were analyzed quantitatively. Results showed that energy conservation and water conservation are obtained simultaneously. The power plant firing high moisture lignite becomes more environmental friendly with higher power generation efficiency and a lower water makeup rate than the one firing low moisture lignite. And further calculation revealed that the air-cooling unit needs no makeup water and even produces some water as it generates power, when the water carrying coefficient is higher than 40g/MJ.

In-situ analysis of volatile products from lignite pyrolysis with pyrolysis-vacuum ultraviolet photoionization and electron impact mass spectrometry

Pyrolytic species of two kinds of lignites (samples A and B) are investigated in-situ with pyrolysis-vacuum ultraviolet photoionization/electron impact mass spectrometry (PVUVPI/EIMS). Mass spectra of pyrolytic fragments are measured during temperature-programmed pyrolysis process of two lignite samples and the intensity profiles of the pyrolytic species are estimated in different temperatures. Experimental results show that H2, H2O, CO, and CO2 are dominant inorganic gaseous products and their characteristic temperatures are in accord with the temperatures of related chemical bonds cleavage. Mononuclear aromatics are dominant organic pyrolysis products, and many olefin species are also identified. The differences between samples A and B on macromolecular structures make the distribution of pyrolytic products different. In addition, the peak of H2S and CH3SH are both clearly observed in mass spectra of sample B, which could come from thioether bonds decomposition. This work also illustrates that the PVUVPI/EIMS performs very well in in-situ analysis pyrolytic products.

Study on the Selected Lignite Using as Organic Carbon in the Treatment of Nitrate Contaminated Groundwater

Twelve kinds of lignite from different areas of China were used for the study of solid-phase biodenitrification. The amount of released carbon, rate of nitrate removal and acute toxicity were examined for all the lignite samples. The results showed that the averaged nitrate removal rates of lignite from Wangniutan and Zhangjiakou were higher than the others, which can reach above 30%. The averaged removal rates of lignite from Zhaotong, Aksu and Faku were more than 20%, and others were less than 10%. Lignite from Wangniutan, Zhangjiakou, Aksu and Faku were more suitable fillers as biodenitrification carbon for its less luminescent bacteria acute toxicity.

Influence of drying on the extraction of different processed lignites

Industrial extraction of montan wax from lignite requires a specific pre‐treatment of raw material concerning milling and drying aiming on particles with sufficient strength and grain size distribution. The wax or its intermediate is a basic material, for example, in foundry, asphalt, or cosmetic industry. First time, the effects of drying temperature and moisture content of lignite samples on extraction rate, extraction yield, and mechanical properties were investigated. The examination was conducted out in lab‐scale with two different mechanical pre‐treatments. The experimental conditions ranged from 85 to 135°C concerning drying temperature and 1–20% for moisture content. The kinetic analysis of analytical wax extraction was made by adopting an approach from natural material extraction by Bucić‐Kojić et al. . The extraction yield as well as the extraction rate is increasing with increasing moisture content until a constant level is reached whereas temperature of drying air showed unexpectedly no significant influence on both parameters. The mechanical properties of the solids were determined by a pressure stress test. For both investigated solids, mechanical strength increases with lowering moisture content. The solids produced with the novel pre‐treatment showed in general a favorable compression behavior than the normally used particles.Practical applications: Industrial montan wax extraction process requires hard lignite particles, which do not decay during processing and handling. The strength of lignite is highly influenced by moisture content besides other factors such as the kind of lignite, the surface mine, drying technology, milling, and processing. The strength of lignite particles increases until a maximum in solidity is reached while drying down from deposit moisture of about 50 wt%. Lignite beds with high moisture content or wide grain size distribution offer the risk of their compression. Such compressed beds are not suitable for extraction due to a lowering or even total loss of permeability for the solvent. The selection of an adequate drying procedure and moisture content of the lignite avoids such problems. But a decrease of moisture content to 1% is known to reduce extraction yield considerably, e.g., the maximal extraction yield requires a specific moisture content of lignite particles .

Moisture Adsorption Properties of Dried Lignite

Moisture adsorption properties of dried lignite were investigated experimentally and mathematically. Three kinds of lignite (Hailaer, Huolinhe, and Indonesia) with different water contents were tested with a machine that maintained a constant temperature and relative humidity. The obtained experimental adsorption data were applied to the Guggenheim, Anderson, and de Boer (GAB), modified Guggenheim, Anderson, and de Boer (MGAB), modified Oswin (MO), modified Henderson (MH), and modified Freundlich (MF) isotherm equations to test their applicability to dried lignite. The order of best fit of adsorption across the entire temperature and relative humidity range was MF > MGAB > GAB > MH > MO. On the basis of the experimental data, the MF equation was modified to consider the effect of the initial moisture content of dried lignite on the equilibrium water. The critical temperature and relative humidity values were obtained with the modified MF equation, which was then used to determine the moisture adsorption occurrence for the dried lignite with a specific moisture content under different environmental conditions. Shanghai and Guangzhou were the target-user locations of the dried lignite. The critical water content values were obtained to avoid the moisture adsorption. These values provided the theoretical guidelines for the target control of the lignite drying process and storage conditions.

Modeling and Experiments for Heat Transfer Process in Pulverized Coal-Firing Furnace With Two-Dimensional Radiation Characteristics

A dimension-reducing method for calculating the radiant heat transfer with two-dimensional characteristics is introduced in this article. Using this dimension-reducing method, the two-dimensional discrete transfer method (DTM) was applied to a cylindrical enclosure where the medium was absorptive and emissive. The two-dimensional DTM was proved to produce equivalent prediction results as the three-dimensional radiation computation. Then the two-dimensional DTM was incorporated into a general pulverized coal combustion model to estimate radiant heat transfer. The temperature distribution and the net heat flux distribution of an axisymmetric pilot furnace, in which three kinds of lignite were burned, respectively, were calculated using the comprehensive model. The prediction using this model has been found to have a high agreement with the measured data, that the temperature errors was at ± 5% and the net heat flux error was at about ± 15%. The results have demonstrated the feasibility and potential of using the two-dimensional DTM for radiation modeling in pulverized coal flame, and confirmed that the dimension-reducing method and the overall model will be simple and convenient for engineers to use.

Petrographic Characteristics of Neogene Lignites from the Ptolemais and Servia Basins, Northern Greece

In this study the petrographic analysis results of Ptolemais and Servia Neogene lignites, Northern Greece, are presented. The geological position, lithotype, and maceral content of these lignites, as well as some chemical parameters and changes in the reflection of different macerals, are described. The interdependence between maceral content and environmental conditions in the process of peat formation is traced. Petrographic analysis shows that coals are represented by different kinds of lignites from dark brown to black, semibright lignites, consisting mainly of the coal lithotype humoclarain, rare strips and bands of bright humovitrain, and dull humodurain. The sample from the Lava deposit in the Servia Basin is composed of grayish to black, dark humoclarain. The predominance of humodetrinite macerals (densinite and attrinite) and the low contents of inertinite show that the lignites in the Ptolemais and Servia Basins are formed in limno-telmatic conditions and in different mire types, being similar to herbaceous swamp, fen, or marsh.

Effects of Humic Acids Extracted from Mined Lignite or Composted Vegetable Residues on Plant Growth and Soil Microbial Populations

Growing interest in the market for humic substances with agricultural applications has led to the development of new potential sources of these compounds other than fossil matrices (e.g. different kinds of lignite), which, until now, have represented the main raw material for the extraction of humus-like products. High quality compost (green compost) obtained through the aerobic biostabilization of selected organic residues, such as vegetable waste from source-collection at garden-produce markets, may be considered for this purpose. Beyond the primary need to develop technically and economically reliable procedures for the extraction of humic substances from compost at the industrial scale, importance must be placed on controlling the influence of such compounds on soil-plant systems. Humates from leonardite, representative of the active agents among humus-based commercial preparations, have been compared in pot trials with humic acids, potassium salts, from green compost in order to evaluate their respective effects on soil microbial activity and plant productivity. Differences between pot blocks amended with humic acids have suggested that humus-like substances extracted from compost seem to exert higher stimulative effects on microbial growth and vegetative biomass production than fossil humates.

Scientific Serials

THE November number of the Geological Magazine (No. 77) opens with an article by the editor, Mr. H. Woodward, on Fossil Crustacea from various formations. The species described and figured by the author are Scyllaridia bellii from the London clay of Sheppey, and Palœga carteri from the lower chalk. One of the most important papers in the number is on the coal-bearing rocks of Southern Chile by MM. Lebour and Mundle. The coal appears to be only a kind of lignite; it is found in beds of tertiary age. Mr. Lucy contributes a paper on the Post-pliocene Drift of Charnwood Forest; Mr. H. F. Hall, a note on the Glacial and Post-glacial deposits in the neighbourhood of Llandudno; Mr. L. C. Miall, a paper on the formation of swallow-holes in mountain limestone; and Mr. E. Wilson, a notice of some altered clay-beds and sections in Tideswell Dale, Derbyshire. The remainder of the number is occupied as usual by reviews, notices, and miscellaneous matter.