Thermal Decomposition Of Coal Research Articles

On the issue of establishing the hazardous properties of mine seams according to the output of coal thermal decomposition products

The article analyzes the principles of building an industrial classification. It is noted that, according to the qualitative selection and quantitative assessment, the classification indicators of metamorphic transformations of the seams, determined by the average values of the analysis of coal samples, do not coincide with their characteristics according to industrial classifications. It is shown that with the intensification of metamorphic processes in the seams from grades D to A, there is a direct proportional increase in the yield of coke and an inversely proportional decrease in the yield of volatile substances. The choice of criteria for the manifestation of hazardous properties of mine seams should be based on the basic definition of the concept of metamorphism - the enrichment of organic matter with carbon and the depletion of other components. The overwhelming content of carbon and a one-sided increase in the organic mass predetermine its main role as the main indicator of metamorphic transformations of seams and coal. This method of determining the degree of metamorphism makes it possible to establish a direct connection between the manifestation of hazardous properties of mine seams and the composition of the transformed organic matter.

Computational and experimental approaches into molecular structure mechanism of ZQV coal and the COx gas releases during pyrolysis

Understanding the structural features of coal and its reactive behaviors in thermal processing is the fundamental to achieve high-efficiency utilization of coal. However, the molecular structural features and the evolution characteristics at atomic scales in thermal processing remain unclear in the microscopic views, particularly for the low-rank coals, which usually exhibits high oxygen content with a variety of oxygen-containing organic functional groups and gets lots of CO/CO2 release during pyrolysis. This research provides a comprehensive analysis of the ZaoQuan vitrinite (ZQV) bituminous coal's structural attributes and its pyrolysis-induced reactivity, which is crucial for optimizing the thermal conversion of low-rank coals. The structural parameters characteristics and molecular structures of ZQV have been revealed based on series of materials characterizations and molecular modeling calculations. The single molecular description of ZQV was conceptualized to be C209H132O41N2 under the average molecular approximation, and the particle models with size about 10 nm was also been obtained. Based on the built molecular models, reactive force field molecular dynamics (ReaxFF MD) simulations then provided insights into the dynamic behavior of molecular structures under pyrolysis conditions. Experimental validation corroborates the computational predictions, revealing a strong coherence between observed gas products and those derived from simulation data. Crucially, this study vividly captures the dynamic migration patterns of oxygen-containing groups during coal's thermal decomposition, thus contributing to the understanding of gasification processes. The release mechanisms for CO and CO2 are systematically dissected, proposing three and two distinct pathways respectively. These findings not only consolidate the molecular narrative of coal's structure and pyrolysis reactivity but also serve as a reliable foundation for interpreting the COx evolution of low-rank coals. Our integrated approach propels the scientific comprehension of coal pyrolysis and is anticipated to inform the development of more effective coal utilization pathways and thermal treatment technologies.

Analysis of the possibility of solid-phase ignition of coal fuel

The article presents the results of theoretical and experimental studies of the ignition process of coal fuel particles in a pelletized state during high-temperature radiation-convective heating in an oxidizing environment. A new, different from the known, “two-temperature” mathematical model of the ignition process of a cylindrical coal pellet under intense heating conditions is presented. During the modeling, a detailed kinetic scheme of the reaction of gaseous products of thermal decomposition of coal with atmospheric oxygen was considered. The mathematical model was tested through a comparative analysis of the theoretical and experimental values of the ignition delay times of coal pellet fuel with experimental data. A wide range of heating conditions that could potentially lead to solid-phase ignition were analyzed. The research results showed that even under conditions of high oxygen content in the original coal, solid-phase ignition of coal pellets does not occur during intense heating. Based on the results of numerical modeling, it was established that the ignition process occurs in the gas phase. The oxygen released during the thermal decomposition of coal is not enough for stable gas-phase or heterogeneous ignition of pyrolysis products in the intrapore space of the fuel pellet. Based on the results of the numerical modeling, it was established that the oxygen released during the thermal decomposition of coal is significantly deficient in the intrapore space. The O2 concentration is not enough for a significant (in terms of heat flow) thermochemical intrapore reaction with gaseous and solid products of thermal decomposition.

Wasteless technology of coal gasification for heat and chemical production

Coal is a conventional source of energy, but its use has recently been restricted because of the environmental standards. Coal is a high-value source for the production of chemicals such as hydrogen, ammonia, methanol, carbamide, etc. The chemicals are produced from synthesis gas in the course of coal gasification. The value of coal as a source for the chemical production also lies in the ampleness of its reserves worldwide while oil and gas reservoirs are available not in all countries. Accordingly, the effective use of coal can contribute to the development of many branches of the chemical industry. The wasteless technologies of coal gasification for the production of heat, synthesis gas, reducing gas for the metallurgy needs and pure hydrogen are described. In these technologies, prior to gasification, thermal decomposition of coal is carried out in a reactor under temperatures up to 700 °C, and the volatile and resinous matters separated from carbon under temperatures of 300–550 °C, after cooling, are used in conformity with their material constitution. The coal gasification flowcharts function in a closed mode, where flows of heated gases first heat coal for the recovery of the associate components of carbon, some heat of the heated gases goes to the production of vapor for the steam gasification of carbon, and the residual heat of gases, up to absorption of СО2 by solutions of alkalis, is used to produce hot water, which reduces external consumption of heat in coal gasification. The proposed methods of coal gasification are low-cost as the by-produced substances and heat of different heated materials are utilized. Moreover, air emissions are absent, thus, the production is ecofriendly and green.

Chemical structure effects on coal pyrolyzates and reactions by using large-scale reactive molecular dynamics

The relationship between the coal chemical structure and its thermal reactivity is vital to understand coal pyrolysis behaviors. In order to explore chemical structure effects on pyrolysis process, five large-scale coal models of different ranks were constructed and simulated with ReaxFF MD simulations by a combined approach of high performance computing and cheminformatics based reaction analysis in this work. The qualitative temperature mapping results between ReaxFF MD simulations and thermogravimetry experiments were obtained for the first time through the detected covalent bond breaking, which suggests a promising scheme to map the simulation results to the real world. Importantly, the typical structures in coal can be used as the indicators to predict pyrolysis stages, weight loss profiles and major pyrolyzate distributions from the atomistic level. The starting temperature of coal thermal decomposition is anchored by the parameters of falO in 13C NMR representing alkyl ether amounts; and the largest phenol tar generation links closely to the faP NMR parameter; meanwhile methoxy groups determine the initial generation of CH3 radicals and CH4 at relatively low temperature. Additionally, the dynamic profiles of Car-Car bonds and the second increasing trend for CH3 radicals have strong relationship with recombination reactions. With the reasonable coal structures, the large-scale ReaxFF MD simulation alone can complement experimental observation comprehensively to understand the complex coal thermal chemistry and used as a preliminary screening approach to select the coal type or rank for industrial utilization.

НАУКОВІ ОСНОВИ РОЗРОБКИ МЕТОДУ ПРОГНОЗУ НЕБЕЗПЕЧНИХ ВЛАСТИВОСТЕЙ ВУГІЛЬНИХ ШАХТОПЛАСТІВ

Purpose: to develop a method of coal gradation to predict the hazardous properties of coal seams during mining. Methodology: based on the study of the interdependence between indicators of the degree of coal metamorphism, which characterize various aspects of its transformation in geological processes. Results: the dependence of the manifestation of any dangerous property of coal seams during mining operations on the influencing factors of the three blocks is considered. In the general case, the most dangerous properties of coal seams include the release of explosive and flammable gases, sudden emissions of coal and gas, the tendency to spontaneous combustion and the occurrence of endogenous fires, increased dust formation, explosiveness of coal dust and other negative phenomena. To prevent emergencies during mining operations, it is necessary to take into account the influence of factors of all three units. Factors of the first block determine the genetic predisposition of mine shafts to the appearance of dangerous properties under the influence of geological processes and metamorphic transformation of the source material. The factors of the second block include mining and geological conditions of coal seams. On the basis of data on parameters of the first two blocks at stages of designing and operation of the coal enterprise, mining indicators of the third block of factors are put. In contrast to the mining-geological and mining conditions of the second block, the factors of the first block are the least studied and not always reliably established. They must determine under the influence of metamorphism changes in the chemical composition, structure and physical properties of coal in the bowels of the Earth, mainly under the influence of elevated temperature and pressure. Currently, more than thirty factors are known, which in different ways characterise the metamorphic transformations of the starting material. There is a practice when in normative documents for the characteristic of degree of metamorphic transformations of layers in the vast majority of cases one indicator is used – an exit of volatile substances at thermal decomposition of coal without access to air. One indicator can not simultaneously and on all sides characterise the content, structure, chemical and physical and mechanical properties of the organic mass of coal and mineral impurities. It is necessary to proceed from the position that each dangerous property of mine layers depends on a certain influence of several factors of metamorphism. Studies have shown that the carbon content directly controls the overall change in the sum of the main components of organic matter (hydrogen, nitrogen, sulphur, oxygen), and the reflection rate of vitrinite – reflects structural changes in petrographic composition. The chemical activity of coal is also affected by the presence of moisture in different states, composition and properties of mineral impurities. The use of each auxiliary indicator must be justified taking into account the purpose of application and the method of its determination Scientific novelty: the carbon content and the rate of reflection of vitrinite in the range of ranking coal by their degree of metamorphic transformations have a reliable quantitative determination, which allows their use in establishing the hazardous properties of coal seams as the main classification indicators. Practical value: the results obtained allow developing general principles of scientific substantiation of the method of forecasting the dangerous properties of coal seams in combination with mining-geological and mining conditions of work on the basis of carbon content and vitrinite reflection index.

СТАТИСТИЧНІ МОДЕЛІ КЛАСИФІКАЦІЙНОГО ПОКАЗНИКА СТУПЕНЯ МЕТАМОРФІЗМУ ВУГІЛЛЯ ДЛЯ ПРОГНОЗУ НЕБЕЗПЕЧНИХ ВЛАСТИВОСТЕЙ ШАХТОПЛАСТІВ

Purpose: Based on statistical models of volatile matter yield during thermal decomposition of coal without air access (Vdaf) to establish probable relative errors of its measurement of absolute values which would allow to use the indicator with predetermined accuracy Vdaf as the primary classification criterion metamorphism of coal beds for the prediction of dangerous properties when led mining. Methods. It is used to create several sets of Vdaf values that have some features that are essential for their characteristics, followed by analysis of the statistical characteristics of these sets with the establishment of differences or similarities between statistical models. Results. Six sets of coal beds, which have different features of their creation according to the Vdaf criterion. There were from 114 to 412 variants in each set. As a general conditionally accepted set of 2091 coal beds of different coal deposits. For all (7) sets tested, the hypothesis of a normal distribution of variants according to Pearson’s criterion χ2 was tested. One part of the sets tested was close to the normal distribution of random variables, and the other did not correspond to the normal law. It is established that one of the reasons for the inconsistency of parts of the population with the normal law is the various errors in determining Vdaf depending on the absolute value of this indicator. In addition, individual samples from the conditionally general population have the same nature of the distribution of relative frequencies: with an increase in Vdaf to 10%, they decrease; in the range from 10 to 40% slightly increase; when Vdaf > 40% – again there is a decrease. Based on the close correlation dependences of the relative standard deviations of the volatile matter yield from the averaging curves, the validity of the possible use of Vdaf in engineering calculations of the forecast of dangerous properties of shafts only at its values more than 15-20% is proved. The possible influence of the distance of the coal sampling site to the boundaries of gas weathering zones and geological disturbances, and the high dependence of coal (more than 20%) on the additional error of Vdaf determination was also established. The established possible error values do not guarantee high accuracy of forecasting the dangerous properties of coal beds when using Vdaf as the main indicator of the degree of metamorphism. Improving the regulatory framework for safe mining of coal seams requires justification and application of other indicators of the degree of coal metamorphism. Scientific novelty: For the first time on the basis of statistical models, ambiguous possible errors in determining the yield of volatile substances during thermal decomposition of coal without air access and the inexpediency of its use to predict the hazardous properties of coal beds in mining. Practical significance. The necessity of using other indicators of the degree of metamorphism to improve the regulatory framework for safe mining of coal beds, which directly reflect the content and properties of coal in the process of geological transformations, has been proved.

ВПЛИВ РЕЗУЛЬТАТІВ АНАЛІЗУ АНАЛІТИЧНИХ ПРОБ ВУГІЛЛЯ НА ТОЧНІСТЬ ПРОГНОЗУ НЕБЕЗПЕЧНИХ ВЛАСТИВОСТЕЙ ШАХТОПЛАСТІВ

Purpose: to establish possible quantitative errors in determining the values of some indicators of the degree of metamorphism without attracting the content of total moisture and mineral impurities to predict the hazardous properties of coal mine layers during mining. Methodology: based on the use of initial data on the quality indicators and properties of coals for specific coal seams, given in the reference sources, with the subsequent recalculation of the state of samples from their dry ashless or ashless state to the raw state. Comparison of the samples of indicators were determined, respectively, using analytical samples and based on the results of recalculation to the initial state (close to the production state), conclusions were drawn about possible errors in the case of using the analysis results of the analytical samples to predict hazardous properties of mines. Results: The analytical state of the samples for dry ashless state (daf) or wet ashless state (af) does not correspond to the state of coal in the working area of mining operations (r), which most accurately characterizes the manifestation of mine hazardous properties. The indicators of the release of volatile substances during thermal decomposition of coals, which are used to predict the hazardous properties of mine coal seams, do not directly reflect changes in the elemental composition of coals during metamorphic transformations. Methods for preparing analytical samples provide for grinding to small fractions, removing external moisture and enriching to ash content less than 10%, which does not correspond to the state of coal (r) in the mining area. The use of indicators set for dry ashless combustible (organic) mass excludes the possibility of analyzing the influence of moisture and mineral impurities on the manifestation of the hazardous properties of coal seams. The use of such indicators to predict the hazardous properties of mine coal seams can lead to errors in their determination of 45 ÷ 50%. The hazardous properties of coal seams can be adequately characterized only by the combined composition and properties of organic matter and mineral impurities in a state close to the presence of coal in the mining area. Using the example of possible significant errors in the calorific value, in the case of its use to characterize the hazardous properties of coal mine seams, the expediency of scientific substantiation of a set of indicators for a reliable forecast of a specific hazardous property for a specific seam formation was proved. Scientific novelty: hazardous properties of coal seams are reliably predicted on the basis of the composition and properties of organic and mineral components, reduced to conditions close to the state during mining operations. Practical value: the results obtained give grounds to scientifically substantiate the selection of the necessary indicators for predicting a specific hazardous property of coal seams and make proposals for improving the regulatory framework for the safe conduct of mining operations.

ПРО ВПЛИВ МІНЕРАЛЬНИХ ДОМІШОК НА ВИЯВЛЕННЯ НЕБЕЗПЕЧНИХ ВЛАСТИВОСТЕЙ ВУГІЛЬНИХ ШАХТОПЛАСТІВ

Purpose: to establish a possible correspondence between metamorphic processes with artificial thermal destruction of coals and their ashing in order to identify the components of mineral impurities that can affect the manifestation of the hazardous properties of coal mine seams. Methodology is based on a comparison of metamorphic processes that took place at a certain temperature mode in the bowels of the Earth and the production of artificial coals and their ashing. Results: The research made it possible to reveal the important role of mineral impurities in the formation of the hazardous properties of coal seams. This is due to both the significant possible content of mineral impurities in fossil coals, and the simultaneous presence of the main components that determine the hazardous properties of coal seams (carbon, hydrogen, sulfur, oxygen and moisture), both in the organic and in the mineral parts of fossil coals. To improve the regulatory framework for the safe conduct of mining operations, it is necessary to take into account features of the properties of fossil coals due to the presence of mineral impurities in them. In modern regulatory documents on the safe conduct of mining operations, in general, several indicators are used without proper scientific justification: the mass yield of volatiles during the thermal decomposition of coal, the volumetric yield of volatile substances, the thickness of the plastic layer and the logarithm of the electrical resistivity of anthracites. Their values are related to the dry ash-free mass of organic matter only. This excludes consideration of the influence of mineral impurities on the manifestation of the hazardous properties of coal mine seams during mining operations. In many cases, the content of moisture and sulfur is a criterion for the manifestation of hazardous properties of coal seams. They belong to the integral components of both organic and mineral constituents of fossil coals. The share of mineral impurities in the coals of individual coal seams can be more than 40%. The presence of oxygen, hydrogen, sulfur and moisture in mineral impurities significantly affects the manifestation of the hazardous properties of coal seams during mining. The content of mineral impurities in fossil coals in engineering calculations can be determined on the basis of the ash content of coals according to known empirical relationships, corrected for the content of total sulfur and, in some cases, carbon dioxide. Scientific novelty: the significant influence of mineral impurities in fossil coals on the manifestation of hazardous properties of coal seams during mining operations has been proved. Practical value: the results obtained allow substantiating the methodology for the combined use of the composition of organic and mineral components of fossil coals for a reliable forecast of the manifestation of hazardous properties of coal seams and improving the regulatory framework for their safe mining.

Investigation into coals of different ranks using FTIR and Raman spectroscopy, X-ray diffraction and thermo-kinetic analyses

Two sub-bituminous (Onyeama mine, Nigeria and Powder River Basin, USA) and one bituminous (CNX Coal Resources, USA) coal samples were subjected to structural and chemical characterisation. The FTIR and Raman spectroscopy, X-ray diffraction and other physico-chemical techniques were deployed for this purpose. The coal ranking and aromaticity were evaluated from specific peaks on the XRD diffractogram. The coal samples were also subjected to thermo-kinetic analysis. The HHV for the coal samples ranged from 26.0 MJ/kg to 33.8 MJ/kg. Relatively, the Nigerian coal demonstrated an exceptionally high surface area, approximately 29.0 m2/g while Wyoming's and Pennsylvania's respectively recorded 0.4 m2/g and 3.9 m2/g. The ratio of band intensities, ID/IG was computed from Raman spectroscopy to be between 0.84 and 0.94 for the coal samples. Furthermore, the kinetics parameters deduced from TGA measurements revealed that thermal decomposition of coal is better modelled as a multi-step reaction mechanism. [Received: August 10, 2019; Accepted: January 13, 2020]

Influence of Cu(NO3)2 Activator and Gas Composition on the Thermal Decomposition of Coal and Lignite

The thermal transformation of coal and lignite in the presence of Cu(NO3)2 activator (5 wt %) is investigated as a function of the atmospheric composition. The copper nitrate is supported on to the samples by the incipient wetness with Cu(NO3)2 solution in water and alcohol. The effect of the activator is studied as a function of the gas (air/argon) composition, by thermogravimetric analysis with heating at 10°C/min in the range 25–800°C, at atmospheric pressure. With change in gas composition, the activity of Cu(NO3)2 changes. Specifically, the thermal transformation is shifted to lower temperature: Δt = 33°C for lignite and 70°C for coal. With increase in oxidant (air) content in the gas, the activity of the added Cu(NO3)2 increases: that is, Δt increases. By mass spectrometry, the gaseous oxidation products of the coal are analyzed. The upper temperature limits on the peaks of nitrogen-oxide (NOx) liberation are determined as a function of the gas composition.

On determining coal classification indicators for establishing dangerous properties of mines

Currently, more than 20 qualification indicators are known by which degree of metamorphic coal transformations are established. Most of these indicators are designed for determining technological properties with industrial use of coal in mind. Due to sufficient knowledge of the indicators used, industrial classifications are constantly being improved. The modern classification by genetic and technological parameters groups the coals by the grades based on ten indicators. Of these, only one - the mass yield of volatile substances during the thermal decomposition of coal - is used as the main indicator of the manifestation of dangerous properties of coal seams without due scientific justification. Dangerous properties of coal seams during mining include: gas content of coal, a tendency to gas-dynamic phenomena and spontaneous combustion, dust forming ability and explosiveness of coal dust. In industrial classifications, the main indicator is determined for the dry ash-free state of organic matter. Manifestation of dangerous properties of coal seams occurs in the presence of both moisture and mineral impurities. This fact is not taken into account by other auxiliary indicators used to predict the hazardous properties of coal seams. Moisture in coal seams is in at least four states, and it is completely removed while analyzing the samples and is not taken into account in volatile products of thermal decomposition of coal. Thus, when using the indicator of mass output of volatile substances, influence of moisture in any form of its presence in coal on the occurrence of emergency situations is automatically ignored. The probability of emergencies during mining is largely determined by the ratio between components of organic mass (C, O, H, S, N) and mineral impurities. It is also not taken into account in normative documents which regulate safety of coal seam mining. The classification indicators defined in different ways characterize different aspects of coal conversion in metamorphic processes. Volatiles yield and average vitrine reflectance, well studied in industrial applications, correspond to different aspects of degree of conversion of starting organic matter. In order to establish dangerous properties of coal seams, their mutual substitution is unacceptable, which is confirmed by nonlinear connection between them. The existence of a genetic relationship between the outburst and fire hazard of coal seams has been established. This indicates the need to develop a unified classification of the hazardous properties of coal seams by genetic, mining engineering and geological parameters. The scientifically substantiated use in regulatory documents of a set of classification indicators that directly characterize the manifestations of the hazardous properties of coal seams will help to reduce number of accidents and injuries in coal mines.

Chemical, phase composition and properties of products of thermal decomposition of coal of Tavantolgoy deposit of Mongolia

Chemical, phase composition and properties of products of thermal decomposition of coal of Tavantolgoy deposit of Mongolia

Co-firing of blends of sugarcane bagasse and coal

The interaction effects between sugarcane bagasse and a Brazilian coal during co-firing were investigated by means of thermal decomposition behavior, comparison between theoretical and experimental results, activation energy, and ignition temperature. The blends were prepared in the ratios of 100:0; 75:25; 50:50; 25:75; 0:100 (bagasse/coal). The interaction effect evaluated in this study was related to the interference of the bagasse volatile matter content in the coal thermal decomposition. The thermal decomposition behavior analyses were performed in a thermogravimetric balance, and the apparent activation energy was determined by two different models—model-free and local linear integral isoconversional method—under two different heating rate ranges. The results showed that the high volatile content of the sugarcane bagasse leads to more intense combustion, lower ignition temperature, and more complex reaction mechanism, as compared to coal. When the fuels are blended, there is a temperature anticipation of the events related to the decomposition of the coal portion in the mixture, the reaction rates increase and the ash formation is affected. The kinetic data also suggested that the interaction between both materials may occur and improve the burnout of the blend in relation to the pure coal firing due to the contribution of sugarcane bagasse volatile matter. Nevertheless, the presence of the bagasse did not allow to lower activation energy during the blends devolatilization process.

Ignition of composite liquid fuel droplets based on coal and oil processing waste by heated air flow

To expand the resource base of fuels and methods of hydrocarbon waste recovery, this paper presents the study of the ignition features and conditions of composite fuel slurries based on wastes from coal, chemical, petrochemical, energy, and transport industries. Composite liquid fuels have been prepared using basic components: filter cakes of low-caking, nonbaking, and bituminous coal; engine, turbine, and transformer oil waste; plasticizer. According to a well-known experimental approach, the investigations of the ignition processes have been performed for single fuel droplets (with a radius ranging from 0.5 mm to 1.5 mm) covering a fast-response thermocouple junction. A heated air flow – the ignition source of a droplet – was formed by a specialized blower and a heater. The air temperature varied within the range of 600–900 K. The oxidizer flow velocity was about 3 m/s. With the help of particle image velocimetry hardware and Actual Flow software, we determined the conditions and characteristics of the oxidizer flow transformation around droplets of various shapes. The typical stages of fuel droplet ignition were identified using high-speed video cameras and Tema Automotive software: heating; the evaporation of water and flammable liquid; the thermal decomposition of coal; the formation and ignition of a gas-vapor mixture; the heating of coke residue; the heterogeneous ignition and combustion of carbon. Further, ignition delay times were determined under the conditions of low temperature (600–900 K) heating, as well as the combustion times of fuel droplets with different compositions. Finally, the minimum temperatures were specified sufficient for the sustainable ignition of composite liquid fuel. The established ranges of minimum temperatures show the possibility of burning fuel slurries based on coal and oil processing wastes in heat and power boilers of different capacity. The temperature modes can be adjusted to the required environmental, economic and energy performance indicators. The maximum temperature of a droplet during the combustion process is more than 1100 K. This result confirms the high combustion heat of fuel slurries, even those based on typical industrial wastes, and shows great prospects of their application in the thermal power engineering. The wide use of abundant industrial wastes as the main fuel components of coal water slurries containing petrochemicals is a high-potential solution to the global problem of their recovery and the reduction of the environmental load of coal-based thermal power engineering on the nature and humankind.

Heat and mass transfer at gas-phase ignition of grinded coal layer by several metal particles heated to a high temperature

Characteristics of gas-phase ignition of grinded brown coal (brand 2B, Shive-Ovoos deposit in Mongolia) layer by single and several metal particles heated to a high temperature (above 1000 K) have been investigated numerically. The developed mathematical model of the process takes into account the heating and thermal decomposition of coal at the expense of the heat supplied from local heat sources, release of volatiles, formation and heating of gas mixture and its ignition. The conditions of the joint effect of several hot particles on the main characteristic of the process–ignition delay time are determined. The relation of the ignition zone position in the vicinity of local heat sources and the intensity of combustible gas mixture warming has been elucidated. It has been found that when the distance between neighboring particles exceeds 1.5 hot particle size, an analysis of characteristics and regularities of coal ignition by several local heat sources can be carried out within the framework of the model of “single metal particle / grinded coal / air”. Besides, it has been shown with the use of this model that the increase in the hot particle height leads, along with the ignition delay time reduction, to a reduction of the source initial temperatures required for solid fuel ignition. At an imperfect thermal contact at the interface hot particle / grinded coal due to the natural porosity of the solid fuel structure, the intensity of ignition reduces due to a less significant effect of radiation in the area of pores on the heat transfer conditions compared to heat transfer by conduction in the near-surface coal layer without regard to its heterogeneous structure.

Thermal stability of ammonium nitrate in high-temperature coal seam

In order to investigate safety of blasting process in high-temperature coal seam, thermal decomposition characteristic of ammonium nitrate (AN) with coal was studied. The characteristic of HTCS was investigated firstly. The results found that organic materials presented in HTCS. TG–DSC results found that the notable exothermic reaction of AN with coal took place. And large amount of residue was found, which showed little amount of coal took part in thermal decomposition reaction. The activation energy results showed the coal was higher than AN. Isothermal experiments showed that AN with coal thermal decomposition is at about 135 °C. RSFTIR experiments found organic materials induced AN reaction at very low temperature. And NO3 − was found in molten AN. TG–MS experiments found that AN with coal thermal decomposition began at 146 °C. The essence of HTCS reaction was reaction between organic materials and HNO3. With temperature elevated, the organic materials were oxidized by HNO3, which caused exothermic and gave rise to premature and misfire in blasting process. The study results have significant implication in the understanding of safety of civil explosives in HTCS.

Primary reactions of lignite-water slurry gasification under the supercritical pressure in the electric field

Lignite-water suspension supercritical gasification was carried out in an electric field with an intensity of 0.5V/cm in the presence of additives under the pressure of 24MPa in two temperature ranges: 330–360 and 390–450°C. From 50 to 78% of hydrogen and oxygen of gas products were of water origin. The application of the electric field switched carbon oxidation over to hydrocracking in the range of the subcritical temperature. At the subcritical temperature, the electric field had moderated the lignite hydrolysis and intensified its hydrocracking.The gasification of lignite-water suspension under the supercritical pressure in the electric field had at least five types of interactions: electrolysis of water, thermal decomposition of coal, carbon oxidation by oxygen of water as well as hydrolysis and hydrocracking of coal. Electrolysis and hydrocracking were dominant for the process at the subcritical temperature on water. Hydrolysis and hydrocracking of CC bonds of coal were the main at the supercritical parameters of water.

The thermal conversion of coal impregnated with ZnCl2

ABSTRACTCoal is a porous combustible solid fuel. The pores can easily absorb the liquid solution of salts. ZnCl2 have the capability to absorb within the pores of coal and causes to increase the roughness of internal pore surface. The chemisorbed ZnCl2 posses the ability to effect the thermal conversion of coal. In this study, catalytic behavior of ZnCl2 for thermal decomposition of coal for low-temperature gasification was studied by varying concentration, time, and temperature.

Maximum combustion temperature for coal-water slurry containing petrochemicals

This study examines the temperature change of droplets of coal-water slurry containing petrochemicals (CWSP). The slurry consists of coal and oil processing waste. The temperature of oxidant in a modelled combustion chamber is varied between 600 and 1200 K. The initial size (radius) of CWSP droplets varied in the range of 0.5–3 mm. The study identifies typical temperature trends at the center and on the surface of the CWSP droplet. The temperature trends represent the following stages: (i) heating of fuel, (ii) evaporation of water and a liquid combustible component, (iii) thermal decomposition of coal and yield of volatiles, (iv) gas phase ignition of volatiles together with vapor of the combustible liquid, and (v) heterogeneous ignition of carbon and its burnout. Moreover, these trends indicate the maximum combustion temperatures of CWSP that reflect corresponding heat release. The study specifies the parameters which influence the maximum combustion temperature: fuel component composition, properties of components, droplet size, and the oxidant temperature. Finally, the study defines the minimum ignition temperatures and delay times of sustainable combustion initiation that characterize the ignition inertia. The knowledge of influence of these factors will allow one to predict the optimal conditions for the combustion of the CWSP.