Coal Ignition Research Articles

Intensification of the Process of Coal Ignition by Adding Biomass under Flame Combustion Conditions

Intensification of the Process of Coal Ignition by Adding Biomass under Flame Combustion Conditions

Kinetic studies of ignition of coal char particle suspension in hot air

Coal ignition has been a focal point in the pursuit of improved energy efficiency and reduced emissions. This study focuses on investigating the kinetic characteristics of char ignition within a closed reactor. The combustion process is modeled using a one-step global reaction in a quiescent air environment. The results show that particle ignition time increases with equivalence ratio and particle size, while decreases with gas initial pressure and initial temperature. Particle ignition temperature is minimally affected by the particle size, slightly influenced by the gas initial pressure and initial temperature, but substantially influenced by the equivalence ratio. In the fuel-rich condition, the coal char combustion exhibits a thermal runaway stage, primarily driven by the escalating particle temperature, followed by a decaying stage, mainly influenced by the depleting oxygen mass fraction. The dominant kinetic factors affecting the heat release rate (HRR) peak are detailly investigated: the HRR peak shows an initial increase and subsequent decrease with the equivalence ratio, which is mainly controlled by the total particle number and particle temperature; Particle size affects the HRR peak through altering the total particle specific surface area, i.e., the product of the particle number and the particle diameter squared; the gas initial pressure and temperature all affect the HRR peak through directly altering the gas density. Additionally, larger retention coefficient leads to faster particle ignition and higher HRR peak. These findings provide valuable insights into the regulations of coal combustion processes, particularly in scenarios involving elevated pressure and temperature, such as coal/mine explosions.

Intensification of the Process of Coal Ignition by Adding Biomass Under Flame Combustion Conditions

The characteristics of thermal decomposition and combustion processes on the heating of fine particles (100–200 m) of Chernogorsky coal, larch wood, and mixtures based on them, including the concentrations of the main components of flue gases (CO, CO2, NOx, and H2S + SO2), were determined using moderntechniques, analytical instrumentation, and experimental equipment. The biomass contents of the fuel mixtures based on coal were 10, 20, and 30 wt %. The temperatures at which the ignition of the coke residue occurred and the combustion process was completed were established using the synchronous thermal analysis of individual solid fuels and their mixtures. Larch sawdust was more reactive than Chernogorsky coal due to the lowest temperature at which the carbon residue was ignited; therefore, the addition of even 10% biomass to coal had a positive effect on the reactivity of the mixture. Under conditions of fuel heating in a flow of air at temperatures of 500–800C, the ignition delay times were determined using a hardware–software complex for high-speed video recording of fast processes. Based on the results of the experimental studies, it was found that the ignition delay times of the test fuels in a flow of heated air varied in a range from 0.02 to 0.22 s, and the addition of 10–30 wt % biomass to coal shortened the ignition delay times of fuel mixtures by up to 50%. The analysis of flue gases upon the combustion of solid fuels made it possible to establish the concentrations of the main anthropogenic emissions; the use of biomass as an additive to coal reduced the emissions of carbondioxide, nitrogen oxides, and sulfur compounds (H2S + SO2) by 2.2–13.5, 6.2–28.9, and 18.2–33.3%, respectively.

Dependence evaluation of factors influencing coal spontaneous ignition

AbstractCoal spontaneous combustion is determined by a variety of factors. Testing can describe the changes incoal spontaneous combustion with various factors, however, the dependence of spontaneous combustion on various factors is unclear. Therefore, reliability theory was used to deduce the functional relationship of the dependence of coal spontaneous combustion on various factors, and construct a model algorithm for predicting the probability of occurrence of coal spontaneous combustion, which is adopted to evaluate and rank the degree of influence of various factors on coal spontaneous combustion. Effective prevention methods are proposed by strengthening the role of the most important factors. The results show that, by taking the duration of coal heating to 150°C as the measurement standard of coal spontaneous combustion, the duration of the initial stage of coal heating increases linearly with the increase of specific heat capacity, thermal conductivity, and moisture content of coal. With the increase of oxygen concentration, oxidation rate, and initial temperature of the coal, the duration of the initial stage of coal heating decreases exponentially. With the increase of gas flow seepage velocity in the coal body, the duration of the initial heating stage changes in a parabolic manner. At the same time, the probability of spontaneous combustion decreases exponentially with the increase of specific heat capacity and moisture content of the coal. The probability of coal spontaneous combustion increases linearly with the increase of coal thermal conductivity, oxygen concentration, gas seepage velocity, and rate of oxidation. The dependence of coal spontaneous combustion probability on different factors can be expressed as follows: coal temperature > gas seepage velocity > specific heat capacity > oxidation rate > oxygen concentration > moisture content > thermal conductivity.

Fuzzy Structured Element Integrated Decision of Metamorphism on Coal Dust Ignition Hazard Rating

To discuss the coal dust ignition hazard rating of different metamorphism, the fuzzy structure element integrated decision model about “no danger”, “weak danger”, “general danger”, and “strong danger” of coal dust ignition is established. 40 kinds of coal samples are selected to carry out coal quality analysis test, overpressure test, temperature test, flame propagation properties test and particle size distribution test. Based on this, coal dust ignition hazard rating decision-making index system is built. The triangular structure element is added to fuzzy comprehensive decision model, by sequencing weighted Hamming distance between fuzzy index value function and fuzzy maximal function, the coal dust ignition hazard rating of different coal quality can be decided. The result shows that: with increasing metamorphic grade, coal dust ignition hazard rating is decreasing, which provides study basis for relation between metamorphism and ignition hazard rating.

Ignition of Coals with Continuous-Wave Lasers at Wavelengths of 450 and 808 nm

The kinetic and energy characteristics of the ignition of microparticle powders of coals of G (gas), Zh (fat), and K (coking) grades with a bulk density of 0.4 g/cm3 under the action of continuous-wave laser radiation at wavelengths λ = 450 and 808 nm with an exposure time of 1 s were measured. Coals were ignited only under irradiation, and the effect of flame propagation was absent. Ignition delay times were measured as a function of the radiation power density, and the critical values of the coal ignition energy density were determined. Energy consumption for the ignition of coals with radiation at λ = 808 nm was greater than that at λ = 450 nm for all grades of coals. It was established that the absorption of laser radiation by coal samples had a quantum character.

Converting Slovianska TPP with the central coal pulverizing plant from anthracite to sub-bituminous coal

Purpose. To develop scientific foundations and technical solutions and to implement the converting of the anthracite boiler of the 800 MW unit of Slovianska TPP with central coal pulverizing plant to sub-bituminous coal combustion with maximum use of existing equipment, without stopping the unit’s operation. Methodology. Theoretical and calculational studies on the processes of coal drying and pulverizing at the central coal pulverizing plant. Calculational justification of technical solutions to eliminate the risk of pulverized coal ignition in the pulverized coal supply system and in the boiler unit burners. Trial tests at the coal pulverizing plant and boiler unit. Findings. The technological features of coal pulverizing plant with steam panel dryers designed for anthracite and the peculiarities of the drying process of an individual coal particle were analyzed. It is substantiated that coal drying at the first stages takes place according to the “wet bulb thermometer” mechanism, and safe conditions for sub-bituminous coal pulverizing are determined and confirmed by tests. Technical solutions to eliminate the risk of pulverized coal ignition in the pulverized coal supply system and in the boiler burners were calculated and implemented, which allows the combustion of different coal grades (anthracite, sub-bituminous coal and their mixtures) without changing the composition of the air duct equipment and burners, using only operational measures. Originality. For the first time, it was proved that coal drying at the first stages takes place according to the “wet bulb thermometer” mechanism, and safe conditions for sub-bituminous coal pulverizing at the central pulverizing plant with steam panel dryers and unventilated ball drum mills were determined. Practical value. Technical solutions were developed and implemented to convert the anthracite boiler of the 800 MW unit of Slovianska TPP with a central coal pulverizing plant to sub-bituminous coal burning with maximal use of existing equipment, without stopping the unit’s operation, including safe modes of sub-bituminous coal pulverizing, as well as pulverized coal of various coal grades and their mixtures feeding and combustion. As a result of the implementation of the developed technical solutions, the 800 MW power unit of Slovianska TPP became the first unit in the world capable of using anthracite and sub-bituminous coal separately or in the form of mixtures of a wide range of compositions.

On the influence of material and shape of the hot particles on the ignition characteristics of coal dust

The multi-field coupling of coal dust ignited by hot particles of different shapes and materials has not been studied in detail, which is an important basis for understanding the multiphase ignition characteristics in the energy industry. The multi-physics coupling method is used to study the solid-gas coupling ignition characteristics. The influence of particles material and shape in a wide temperature range on the ignition characteristics of coal dust is studied. The results show that as the temperature of the hot particles decreases from 1400 K to 1100 K, the ignition delay time increases exponentially in the range of 0 s–1.8 s. The thermal energy and thermal conductivity of hot particles have a positive impact on coal dust ignition. The minimum ignition temperature is 1150 K for metallic particles and 1250 K for non-metallic particles. For the same thermal conductivity, the minimum ignition temperature is positively correlated with the thermal energy of the hot particles. In addition, as the hot particles temperature decreases, the hot spots move from the side to the top of the hot particles. The characteristics of multiphase coupling ignition under different hot particles conditions discussed have certain significance for energy security utilization.

Effect of the primary oxidizer stream jet velocities on the ignition and combustion characteristics of pulverized coal under MILD oxy-coal combustion conditions

MILD oxy-coal combustion technology is a prospective technology with the potential for CO2 capture and storage, and it is characterized by the intense flue gas recirculation to preheat the fuel and to dilute the oxidizer due to the oxidizer or fuel jet with high velocity. The effect of the primary oxidizer stream jet velocities ranging from 1.7 m/s to 11.2 m/s on the coal ignition and combustion characteristics were experimentally investigated on a flat flame pulverized coal burner at various oxygen concentrations of 5%-21% and gas temperatures of 1473–1873 K under O2/CO2 and O2/N2 atmospheres. The coal flame images were recorded by the digital camera, and the flame structure evolution and ignition delay times of coal particles were analyzed at different primary oxidizer stream jet velocities and hot coflow conditions. The coal combustion radiation spectrum was monitored by an optical fiber spectrometer and the coal particle temperatures were derived with the two-color pyrometry. The results showed that the bright yellow soot flame gradually disappeared with the decrease of O2 concentration when CO2 replaced N2. The difference of ignition delay times between O2/CO2 atmosphere and O2/N2 atmosphere decreased from 2.8 ms to 0.2 ms when the primary air jet velocity increased from 1.7 m/s to 11.2 m/s at 1473 K and 5% O2. This meant the elevated jet velocity was beneficial to offset the delayed effect of the physicochemical properties of CO2 on coal ignition. The peak coal particle temperature increased by 68 K at 1873 K and 5% O2 under O2/CO2 atmosphere with the highest jet velocity owing to the accelerated diffusion of O2 into coal particle stream. Moreover, a dimensionless coal particle temperature parameter η was proposed to characterize the variation of the peak coal particle temperature caused by the improved heat transfer and mass transport between the coflow and coal particles under high jet velocity. The maximum value of η was 1.053 at 1873 K and 21% O2 under O2/CO2 atmosphere with the jet velocity of 11.2 m/s, indicating the increased jet velocity had the predominant effect on the increase of peak particle temperature at high gas temperature and O2 concentration.

Ignition of Coals with Continuous-Wave Lasers at Wavelengths of 450 and 808 nm

Ignition of Coals with Continuous-Wave Lasers at Wavelengths of 450 and 808 nm

Numerical and Experimental Investigation of the Decoupling Combustion Characteristics of a Burner with Flame Stabilizer

In order to integrate renewable electricity into the power grid, it is crucial for coal-fired power plant boilers to operate stably across a wide load range. Achieving steady combustion with low nitrogen oxide (NOx) emissions poses a significant challenge for boilers burning low-volatile coal in coal-fired power plants. This study focuses on developing a decoupling combustion technology for low-volatile coal-fired boilers operating at low loads. A three-dimensional numerical simulation is employed to analyze and optimize the geometrical parameters of a burner applied in a real 300 MW pulverized coal fired boiler. Detailed analysis of the burner’s decoupling combustion characteristics, including stable combustion ability and NOx reduction principles, is conducted. The results indicate that this burner showed three stages of coal/air separation, and the flame holder facilitates the stepwise spontaneous ignition and combustion of low-volatile coal. By extending the time between coal pyrolysis and carbon combustion, the burner enhances decoupling combustion and achieves low nitrogen oxide emissions. Based on optimization, a flat partition plate without inclination demonstrates excellent performance in terms of velocity vector field distribution, coal air flow rich/lean separation, combustion, and nitrogen oxide generation. Compared with the initial structural design, the average nitrogen oxide concentration at the outlet is reduced by 59%.

Effects of moisture on soot generation and ignition of coal particle: Investigation and evaluation with OH-planar laser induced fluorescence

Coal with a high moisture content is increasingly being utilized in power generation. However, the influence of moisture on coal ignition and soot generation characteristics remains unclear. Understanding the effect of moisture on coal ignition and soot generation characteristics is important for improving energy efficiency in coal utilization. The characteristics of soot generation and ignition of lignite coal including different contents of moisture (0%, 5%, 10%, 15%) were studied with Planar Laser Induced Fluorescence of OH radicals (OH-PLIF) on a novel concentrating photothermal platform. The results showed that the ignition delay time (tign) of coal and observed soot generation during volatile combustion by the observation of flame luminosity both increased as the moisture content of the coal particles increased from 0% to 15%. The observed increase in tign corresponded to the decreased OH intensity during the ignition. Similarly, the increased generation of soot during volatile combustion corresponded to the increased OH intensity resulting from increased moisture content in the coal. Before ignition, the steam surrounding the coal particle inhibits the release of volatiles. Thus, the formation of fuel molecules (RH) is reduced. Simultaneously, the inhibitory effect of moisture on RH leads to a decrease in H atoms, which further results in a decline in OH radical concentration resulting from the reaction H + O2→OH + O. The combined effect of reduced RH and OH concentrations inhibits ignition for coals containing moisture. During volatile combustion, although OH is commonly acknowledged as the primary oxidant for soot, the increase in OH facilitates gasification reactions, thereby promoting the massive release of volatiles. These volatiles, through processes such as nucleation reactions, contribute to the formation of an increased amount of soot, consequently resulting in an elevated formation of soot in coal with higher moisture content.

Effect of moisture on microwave ignition of bituminous coal.

The interaction between water and microwave is of vital importance to reveal the microwave ignition mechanism of water-bearing coal. This study used two group of bituminous coal after drying and water saturation treatment, for experimental testing and contrastive analysis. During the experiment, permeability of coal samples was obtained based on nuclear magnetic resonance(NMR) test, then different power of microwaves were applied to coal samples, and the occurrence of hot spots within coal samples was regarded as a sign of microwave ignition. Microwave ignition of water-saturated coal is mainly affected by microwave power and coal permeability. The pore water in low permeability coal is conducive to microwave ignition, while the pore water in high permeability coal will prolong the ignition time. There is a permeability threshold, above which the average ignition time of water-saturated coal samples is longer than that of dry coal samples, but below which the opposite is true. These insights can be used to evaluate the safety of microwave technology when applied to coal engineering.

Combustion Characteristics of Lignite Carbonizate and the Possibility of Using It as Power Plant Fuel

The involvement of high-calorific fuel, such as carbonized coal, in the country’s fuel and energy balance can have a beneficial effect on the overall saving of solid fossil fuel resources in the production of heat and electricity. To this end, a comparative analysis was carried out, including determination of the main combustion characteristics of Borodino coal and carbonizate obtained by partially gasifying Borodino brown coal at temperatures of 700–800°С in a batch reactor. To do so, the thermal and elemental composition of fuels was determined, and a qualitative assessment of fuel particle surfaces was carried out using the scanning electron microscopy method. Using the thermogravimetric analysis method, the following parameters of coal and lignite carbonizate were determined: the coke residue ignition and burnout temperature, the maximum combustion reaction rate, the mass variation rate at different combustion stages, the exothermic and endothermic reactions intervals, and the maximum heat flux intensity. The effect the release of volatiles has on the combustion process in the course of heating has been noted. It has been shown that the coal carbonizate ignition temperature is by 30% higher than that of coal; the burnout temperature is by 25% higher, whereas the carbonizate specific heating value is 1.8 times higher than that of coal. The accomplished assessment of carbonizate properties has demonstrated the possibility of its use at thermal power facilities as supplementary power plant fuel.

Meticulous Graded and Early Warning System of Coal Spontaneous Combustion Based on Index Gases and Characteristic Temperature.

The accurate prediction of coal spontaneous combustion (CSC) in the goaf areas of coal mines is a vital aspect of the migration from passive to active fire prevention and control. However, CSC is highly complicated and existing technologies cannot accurately monitor coal temperatures over wide expanses. Thus, it may be beneficial to assess CSC based on various index gases produced by the reactions of coal. In the present study, the CSC process was simulated by temperature-programmed experiments, and the relationships between index gas concentrations with the coal temperature were determined using logistic fitting functions. CSC was divided into seven stages, and a coal seam spontaneous ignition early warning system involving six criteria was established. Field trials demonstrated that this system is a viable approach to predicting coal seam fires and meets the requirements for the active prevention and control of coal combustion. This work establishes an early warning system based on specific theoretical guidelines that permits the identification of CSC and the implementation of active fire prevention and extinguishing measures.

Pure oxygen condition forced oxidation ignition process of underground coal gasification

AbstractUnderground coal gasification without shaft is a technology that uses directional drilling technology to gasify deeply buried coal. The technology first needs to ignite the coal seam during drilling, but as the depth of the coal seam (drilling) increases, it is very difficult to ignite the underground coal seam. In order to ignite the underground coal seam more safely and effectively, the forced oxidation ignition technology has been developed; that is, the coal seam is heated by hot oxygen, and the coal seam is rapidly oxidized and released to ignite the coal seam. Due to the complex confidential environment, it is challenging to ignite underground coal seams. To ignite the underground coal seams more safely and effectively, this paper used a self‐made reactor to simulate the forced convection heating of the bituminous coal under different oxygen flow rates with hot oxygen and used a Fourier transform infrared spectrometer flue gas analyzer to detect the outlet gas, used ATR‐FTIR spectrometer to analyze the solid residues in different areas, and recorded the time and maximum temperature of coal ignition under other processes. The results showed that low‐flow high‐temperature oxygen could quickly burn coal seams. When the oxygen flow rate was 2.5 m3/h, and the coal seam was ignited when heated to 130°C for 170 min. Through GC‐MS analysis of nine flammable components in the tar components under different processes, the content of short‐chain aliphatic hydrocarbons in the tar decreases, and the content of benzene series tends to increase. Through ATR‐FTIR analysis, the solid sample near the gas injection port contained fewer oxygen functional groups; the middle of the furnace body included the most oxygen functional groups; near the gas outlet contained more oxygen functional groups than the raw coal. CO2 would rise to 3% when coal was about to ignite.

INVESTIGATION OF IGNITION AND THERMAL DECOMPOSITION OF COAL FUEL, WASTE AND SAWDUST OF DIFFERENT DEGREES OF METAMORPHISM BASED ON MACHINE LEARNING METHODS

An experimental study of the thermal decomposition of coal fuel, waste, and sawdust of different degrees ofmetamorphism using a simultaneous thermal analyzer (STA) has been carried out. The heating rates in STA experiments were set at 5°C/min, 10°C/min, 20°C/min, and 30°C/min. A comparative analysis of machine learning algorithms for predicting the thermal decomposition of coal fuel is shows that a mathematical model based on an artificial neural network model can accurately simulate thermogravimetric (TG) mass loss curves for various fuels and refined products with an average coefficient of determination of 99%.

ФРИКЦІЙНІ ЯВИЩА У ВУГІЛЬНИХ ШАХТАХ: ПРИЧИНИ, НАСЛІДКИ ТА ВПЛИВ НА ГАЗОДИНАМІЧНІ ЯВИЩА

Coal mines are objects of increased danger, since dynamic, gas-dynamic and thermal phenomena occur in them. These phenomena lead to violations of the operating regime, the failure of mining equipment, the death of miners, an increase in the cost of coal mining and other consequences. The purpose of the article is to present the results of studies of the conditions for the formation of thermal effects in coal mines and the reasons for their occurrence, which has both scientific and applied relevance. The conducted studies made it clear that sparking can occur under the influence of both man-made and natural factors. Friction phenomena leading to thermodynamic effects have been recorded in many mines and countries of the world. The main part of explosions and fires of methane occurs during frictional sparking of rocks containing sulfides. The latter produce sparks of a sufficiently high temperature, which can lead to the ignition of combustible gases, as well as the release of hydrogen sulfide, which has a low ignition temperature. In world practice, cases of ignition of combustible materials during the landing of the roof in the absence of coal have been described. British researchers concluded that the methane-air mixture can be ignited by a spark generated by the friction of sandstone against sandstone or mudstone against sandstone. According to the literature data, the ignition of combustible materials and coals can occur as a result of: emissions and explosions, rock collapse during landing, when a spark discharge occurs in quartz during a tribo- or piezoelectric effect; the presence of sulfides in coals or rocks, pyroelectric effect; electrification of coals. At the micro level, in quartz grains of sandstones, the formation of static charges by dislocations, which are decorated with dust, has been established. A particularly strong effect can occur if, in addition to methane, carbon monoxide, hydrogen, hydrogen sulfide, and acetylene are present in the air. An increase in sparking during frictional friction of quartz in the presence of coal dust has been established. The presence of gas inclusions in sandstone minerals during shear deformations leads to the appearance of additional concentrations of hydrocarbons. As a result of contact of such a mixture with a heated area, a short-term small flash occurs, which is a spark.

АНАЛИЗ СВОЙСТВ УГЛЕЙ И ВЫДЕЛИВШЕГОСЯ ГАЗА ПРИ ОПРЕДЕЛЕНИИ ИХ ГАЗОНОСНОСТИ И СКЛОННОСТИ К САМОВОЗГОРАНИЮ

The high methane content in the coals prevents the penetration of oxygen inside and, consequently, their active oxidation and spontaneous combustion. The paper evaluates the composition of the gas released from coal to determine the gas content of coal and to assess the gas components responsible for coal ignition. It is shown, that in order to safely conduct mining operations, it is necessary to comprehensively analyze the composition of gas released from coal. The results can be applied in forecasting and preventing the occurrence of gas dynamic phenomena.

Research of combustion of solid fuel mixture based on coals of different degrees of metamorphism in the regions of Yenisei Siberia

THE PURPOSE. Consider the combustion process of two coals of different degrees of metamorphism and their mixtures using thermogravimetric analysis based on the change in mass and the rate of change in mass during the heating of fuels. Determine the main characteristics of fuels and the combustion process (temperature of ignition and burnout of the coke residue). Determine the tendency to slagging of coal mixtures. METHODS. When solving the tasks, the thermogravimetric method (TGA). RESULTS. The article provides a brief overview of the combustion of non-design fuels at thermal power plants. The results of technical and elemental analysis of Chernogorsk bituminous coal and Balakhta brown coal are presented. A technique for determining the ignition temperature and burnout of the coke residue is described. The thermograms of the combustion process of two coals of different degrees of metamorphism and their mixtures are presented. The main characteristics of their combustion have been determined. A qualitative analysis of the surface of fuel particles for the presence of pores and cracks is shown. The calculation of the tendency to slagging of coal mixtures has been carried out. CONCLUSION. Thermogravimetric analysis showed an earlier ignition of the Balakhta brown coal in comparison with the Montenegrin bituminous coal. With an increase in the proportion of Balakhta coal in the coal mixture, the profile of the combustion curves shifts to the region of lower temperatures. The addition of 25% Balakhta coal reduces the ignition temperature of Chernogorsk coal by 16%, with an increase in the proportion of Balakhta coal in the mixture, the ignition temperature does not change. Balakhta coal has a high tendency to slagging furnace walls, in contrast to Chernogorsk coal, therefore, an increase in its mass fraction in the coal mixture increases the tendency to slagging furnace screens.