Fragmentation Of Coal Particles Research Articles

Effect of acid concentration on organic structure and small molecule stripping of coal during acid treatment and electrolysis for hydrogen production

Coal-assisted water electrolysis for hydrogen production can effectively reduce electricity consumption and improve the economics of electrolytic hydrogen production technology. However, the influencing factors of this process, especially the mechanism of the electrolyte itself on the coal particles, are not clear. The influence of electrolyte on the electrooxidation process of coal particles is of great importance in practical applications. In this paper, detailed controlled experiments were designed to investigate the effect of electrolyte concentration on coal-assisted water electrolysis. And the laws of the acid leaching and electrooxidation processes on the macrostructure and organic structure of coal particles were investigated by various characterization methods. Information on the small molecules of organic matter stripped from coal molecules under different experimental conditions was also obtained by GC–MS. The results showed that the reactivity of coal particles decreased with increasing electrolyte concentration, and judging reactivity from current density alone would produce some errors. The rebound of current density in high concentration of sulfuric acid mainly came from more fragmentation of coal particles. The CO structure played a facilitating role in the oxidation of coal, while the CO and COOH structures would hinder the further oxidation of coal particles due to their stability. Small organic molecules were released from coal particles into the electrolyte during acid leaching and electrolysis, and the amount of small organic molecules detached was positively correlated with sulfuric acid concentration and oxidation charge, where oxidation detachment dominated.

Failure Mechanism of Gas-Bearing Coal during Outburst and a New Method for Outburst Prediction.

Coal and gas outbursts are among the most serious disasters affecting the safety of coal mines. Gas is an important factor in these types of disasters. To analyze the characteristics of the damage caused by gas to the coal body during the sudden release of the gas process, a self-developed high-pressure gas release cause coal particle ejection experiment device was used to conduct gas release experiments under different conditions. The results show that at the moment of gas release, coal particles and gas are ejected at high speed, crushing coal particles into smaller particles. With the increase in gas pressure and gas adsorption performance, the crushing effect will increase. Also, the coal ejection strength (CES) will increase nonlinearly. By analyzing the mass ratio of ejected coal particles, based on the theory of crushing work and energy, we developed a new coal particle fragmentation index, which can be fitted linearly to CES. The index is based on the f value, which makes up for the limitations of the forecasting method, and can be used more flexibly to predict the coal sample crushing situation. Moreover, the fitting parameter values can more accurately describe the coal particle crushing grade.

In-situ investigation of coal particle fragmentation induced by thermal stress and numerical analysis of the main influencing factors

Particle fragmentation influences thermochemical coal conversion processes in different ways, which is of great significance for process design and control. Different mechanisms are proposed for fragmentation characterization, but direct and substantial optical evidence supporting these theories is rarely reported. In the present study, the fragmentation process of two anthracites with low volatiles is investigated in-situ with the aid of an optical system. The observed fragmentation phenomenon confirms that the thermal stress is the main driving force for the fragmentation of the investigated anthracite particles. Together with a model analysis, a fragmentation pattern different from previous reports is proposed. The tensile stress causes the particles to fragment from the center. Fine particles are produced by multiple tensile failure rather than by the spalling of particles’ outer shell caused by compressive stress. Based on the model, the impact of various process- and particle-related factors on the maximum thermal tensile stress and its appearance time are quantitatively evaluated, which significantly reduces the required time and effort in comparison to experimental analysis of the fragmentation. This study provides direct visual evidence and numerical validation of the fragmentation mechanism, which can be utilized to predict the coal particle behavior and the resulting particle size distribution.

Primary Fragmentation Behavior Investigation in Pulverized Coal Combustion with High-Speed Digital Inline Holography

Comprehension on the primary fragmentation of coal particles is important in understanding and optimizing practical coal combustion and creating credible combustion models. High-speed digital inlin...

Research in the fluidized bed combustion in the Laboratory for thermal engineering and energy - Part A: Achievements in targeted fundamental research

The paper gives a review of the most important results of extensive targeted fundamental research program on fluidized bed combustion in the Laboratory for Thermal Engineering and Energy of the VINCA Institute of Nuclear Sciences. The paper presents a detailed overview of research activities from the beginning in the second half of the 1970'' up to present days. Starting with the motives for initiating the investigations in this field, the paper highlights various phases of research and points out the main results of all research activities, not only the ones that are focused in this paper. Targeted fundamental research topics that are overviewed in this paper are heat and mass transfer, coal particle fragmentation, char particle combustion, sulfur self-retention by coal ash itself, as well as circulating fluidized bed modeling.

Relationship between the tensile strength of irregularly shaped coal particles and various fuel properties

To gain a better understanding of inner-stress-induced coal particle fragmentation during coal utilization processes, the tensile strength of small and irregularly shaped coal particles was investigated, using eleven kinds of coals in the size range of 0.8–6.3 mm. It was found that the tensile strength significantly depends on particle size. As the particle size increases, the tensile strength asymptotically decreases, and the correlation between them could be described by a power function, requiring only different parameters for different coals. In addition, the effects of various fuel properties on the tensile strength are discussed. Coals with medium volatile matter content show the highest tensile strength, and the tensile strength generally increases with rising ash content and decreasing porosity. Based on the obtained results, a simplified model for the approximation of the tensile strength is developed involving the particle size and different fuel properties. A correlation analysis has exhibited that the number of required fuel parameters can be reduced to only two independent ones. This makes the tensile strength of coal particles directly predictable from the proximate and ultimate analysis of coals. With the aid of this prediction model, a better description of conversion processes may be achieved.

Experimental investigation on fragmentation initiation of mm-sized coal particles in a drop-tube furnace

The investigation of mm-sized coal particle fragmentation initiation is of practical interest because of its great importance in the analysis of coal utilization processes such as combustion or gasification in fluidized-bed reactors. Fragmentation experiments were conducted within a drop-tube furnace with eleven kinds of coals of different sizes, and the influences of different factors were discussed. The fragmentation index increased monotonically as the temperature and particle size increase, and the heating rate at different conditions was estimated. No significant correlation was revealed between the fragmentation and the volatile matter, and the thermal stress was deemed to be the main cause of fragmentation. The influences of porosity and tensile strength on fragmentation were more pronounced. Generally, the fragmentation tended to be less extensive as the porosity and tensile strength increased. Accordingly, a parameter consisting of porosity and tensile strength was proposed and defined as the fragmentation resistance number (FRN). The results showed that the larger the FRN is, the more difficult the particles are to fragment; furthermore, the FRN was found to apply well for predicting the fragmentation initiation temperature (FIT) and evaluating fragmentation.

Discrete Element Simulation of Conical Pick’s Coal Cutting Process under Different Cutting Parameters

To explore how the cutting parameters affect the conical pick’s cutting force in coal cutting process, some simulation tests were carried with EDEM based on analysis of coal cutting process of conical pick and micro mechanical characteristic of coal particles. In this paper, traction speed, drum angular velocity, and installation angle of conical pick were considered as the main coal cutting parameters. The discrete element simulations were conducted under 7 sets of various cutting parameters, which were determined in the range of empirical parameters. From the results of the simulation tests, it can be concluded that the fragmentation of coal particles appears in a compacted, squeezed, and crumbling state in coal cutting process; the traction speed has the greatest impact on the conical pick’s cutting force and cutting force fluctuation and the influence of drum angular velocity and installation angle reduce in turn; the force and force fluctuation tend to decrease and obviously increase, respectively, with the increase of drum angular velocity and traction speed; and they will reach the minimum when the pick’s installation angle is 45° under certain traction speed and drum angular velocity.

Shock wave induced primary thermal fragmentation of coal particles

Coal particles when subjected to shock waves can undergo rapid fragmentation, pyrolysis, and combustion, causing enhanced process intensity and efficiency. Particle fragmentation plays a crucial role in this process. Exposure of coal particles to a shock wave is modelled in the present work as combined convection and radiation at the surface and conduction in the interior. Local temperatures within a coal particle and the corresponding thermal stresses are computed to study particle failure. Particle fracture is modelled by a three-parameter Weibull probability to predict the failure location and time. Simulations indicate that pulverized coal of size up to 250 mu m subjected to a shock wave for varying operational, thermal, and physical parameters can experience initial failure within 150 mu s. Particles of size d ae 50 mu m or higher wave strengths (with Mach numbers M ae 5) mostly trigger exfoliation, while interior fragmentation dominates at smaller sizes (d ae 25 mu m). An initial fracture study reveals that pulverized coal with predominant sizes d ae 100 mu m and the coal rank from lignite to bituminous coal is potentially suitable for detonation combustion in waves at Mach numbers M = 3-6. Coal particles under continuous exposure to post-shock conditions undergo recursive exfoliation until the core is 20-40 mu m, after which an interior fragmentation phase is seen until the core is about 1-3 mu m. Much finer coal particles, of the order of internal fragmenting cores, are hardly fractured due to low thermal stresses caused by rapid uniform heating. The fracture model approach for studying shock-induced combustion is validated by a reasonable match of the computed ignition delay with experiments. The fragmentation history indicates a substantial increase in the particle surface area and temperature under shock exposure, as against conventional combustion, leading to an increased order of the burning rates at the onset of ignition, which can sustain through the entire burning phase.

Shock Wave Induced Primary Thermal Fragmentation of Coal Particles

Shock Wave Induced Primary Thermal Fragmentation of Coal Particles

Numerical Simulation of Primary Fragmentation of Coal Particle Mixture Subjected to Shock Wave

ABSTRACTPrimary fragmentation of coal plays an important role in overall combustion efficiency. In practice, a mixture of different sized coal particles is used. Numerical simulation of primary fragmentation of coal particle mixture subjected to shock wave is studied in this work. Coal particles behind shock wave undergo heating, volatilization, and fragmentation. Each of these is modeled in the simulation. Heat transfer is linked with volatilization and solid mechanics to predict primary fragmentation of coal particles using a probabilistic and statistical approach. Fracture time and fracture location are identified by setting fracture criteria, which is obtained using failure probability calculated from Weibull’s Weak Link theory. Irregularities inside a coal particle are included through Weibull’s parameters. Average fracture time of mixture of coal particles is calculated. Numerical results suggest that approximately 90% of coal particles in the mixture have fractured in about 1–2 ms. Simulation results suggest that in the timescale of interest thermal stress dominated, with only marginal effects due to volatilization.

Beneficiation of Indian coals using Ionic Liquids

The interaction between five different Ionic Liquids (ILs) and four Indian coals from the mineral rich eastern part of the country were carried out to identify its dissolution and swelling characteristics. Five ILs consisting of different cations namely: 1-butyl-3-methylimidazolium hexaflurophosphate [BMIM][PF6], 1-butyl-1-methylpyrrolidinium methyl carbonate [BMPYR][CH3CO3], 1-butyl-4-methylpyridinium tetrafluoroborate [BMPY][BF4], tributylmethylphosponium methylsulfate [MTBP][MeSO4] and tributylmethylammonium methylsulfate [TMA][MeSO4] were used. Morphological studies before and after heating the coals in ILs were carried out to determine the extent of swelling and fragmentation of coal particles. Using Fourier Transfer Infrared Spectroscopy (FTIR), the functional groups of ILs in untreated and ILs pretreated coal were identified. An overall 47.6%, 55.6% and 68.1% reduction in the peak area of hydroxyl group (phenolic and free hydroxyl radical) was observed for the ILs [BMIM][PF6], [BMPY][BF4] and [BMPYR][CH3CO3] for the bituminous coal respectively. From the proximate analysis, the increase in fixed carbon content (on weight basis) was found to be 1/3rd as compared to the raw coal. Among the ILs studied, [BMPYR][CH3CO3] was found to have a highest swelling ratio of 1.5. This was also confirmed from the FTIR spectra and the measurement of swelling ratio. Following a similar trend, the morphological studies also concluded that the IL [BMPYR][CH3CO3] was most effective in disintegrating the coal particles to micrometer size. Also this IL gave a total yield extraction of 27.41% (on daf basis) for coal 2 (bituminous) and 35.13% (on daf basis) for coal 4 (lignite).

Direct optical observation of coal particle fragmentation behavior in a drop-tube reactor

An experimental plant – called Single Particle Disintegrator (SPaltor) – is presented that allows an observation of coal particle fragmentation during the thermochemical conversion process. The SPaltor is a lab-scale drop-tube reactor which runs at atmospheric pressure and temperatures up to 1600°C. A high-speed camera, a long-distance microscope, and a high-power LED outside the reactor in combination with two mirrors arranged inside the reactor in a 45°-position are used to monitor the inside of the reactor. In this setup, the particle behavior of three different feedstocks were recorded at nitrogen atmosphere. Two recordings are presented in this paper for a reactor temperature of 1400°C. While a brown coal particle shows no fragmentation, but a bright gas tail due to devolatilisation, an anthracite particle disintegrates into smaller fragments in the first third of the heated zone. For detailed investigation of primary fragmentation, three non-swelling feedstocks were used: A brown coal from Germany, a high-volatile bituminous coal from South Africa, and an anthracite from Germany. Two key figures were used for the description of fragmentation behavior: Fragmentation probability and fragmentation number. The influences of temperature (800–1400°C), particle size (0.8–3.15mm), reactor height (0–90cm), and calculated residence time (0.25–0.5s) were investigated. Increasing these parameters led to an increase of fragmentation of the anthracite and the high-volatile bituminous coal. In contrast, fragmentation was never observed for the brown coal in any experiment. For the chosen particle sizes, the residence time in the heated zone is smaller than 0.5s and comparable to free-fall conditions. The heating rate referring to the particle center varies heavily with particle size and coal type.

The effect of particle size on the strength parameters of German brown coal and its chars

An experimental study on the compressive strength and Young’s modulus of German brown coal from Schleenhain mine was carried out in order to determine the non-empirical mechanical properties required for the development of close-to-reality models of the stress-induced fragmentation of coal particles. A series of uniaxial compression tests was conducted on irregularly shaped coal specimens with diameters in the range of 0.8–6.3mm, which are typical for industrial-scale coal utilization processes. According to the test results, the compressive strength and Young’s modulus of coal particles significantly increase as the specimen size decrease. The data obtained show reasonable agreement with results published in the literature. Additionally, the mechanical properties of chars produced by coal pyrolysis at temperatures in the range of 400–1000°C were measured in order to quantify the influence of the thermal treatment on mechanical properties. The compressive strength and Young’s modulus of the chars increase to a maximum at a thermal treatment temperature of about 800°C and then decrease as the temperature further increases.

Detonation initiated disintegration of coal particle due to the maximum strain energy theory

Fragmentation behaviour of coal particles subjected to detonation wave is being studied. Detonation wave is initiated by a plasma cartridge at one end of a detonation tube. Coal particles are subjected to a shock whose temperature depends on the Mach number of the detonation wave. Temperature shock is found to generate thermal stresses which may fragment the coal particles. A non-dimensional mathematical model for the heat transfer process in the coal particle is proposed. Thermal stresses are calculated at various times and radii while maximum strain energy theory is used to understand the failure behavior viz., the time, temperature and location of fracture. A physical model for coal particle fragmentation when subjected to detonation wave is also proposed. The study suggests that detonation combustion of coal is qualitatively different from conventional method.

Pyrolysis Behavior of Large Coal Particles in a Lab-Scale Bubbling Fluidized Bed

The results of pyrolysis of coal particles with size ranging from 2 to 14 mm in a bubbling fluidized bed are presented in this paper. The investigation is focused on the effect of the coal particle size and pyrolysis temperature on the product distribution and devolatilization time. Fragmentation of coal particles was observed during pyrolysis. It is found that the extent of fragmentation is more serious for larger coal particles at high temperatures. This leads to a quite different variation trend of the yields of pyrolysis products with temperature between the small and large particles examined in this work. No significant effect of the particle size was noticed at low temperatures because the secondary reaction is not active. The devolatilization times of the coal particles tested in this work can be described with the classic particle size power law relation: t = Ad(p)(n). However, the value for the exponent n is much smaller than those obtained by previous researchers, which could be attributed to the fragmentation of coal particles and relative low fluidization velocity employed in this work.

A semidetailed model of primary fragmentation of coal

A mathematical model has been developed to predict the primary fragmentation of coal particles under a wide range of heating conditions as a consequence of thermal stress and of overpressure generated by volatiles.The model calculates the temperature and devolatilization profiles within the particle during heat up, the stress profiles that arise within the particle as a consequence of temperature gradients and volatiles pressure, the probability, timing and mode of fragmentation of the particle based on Weibull theory [13]. Gradual transition from the chemico-physical properties of the original coal to those of the incipient char is allowed for. The model is used to interpret experimental results of primary fragmentation under different heat treatment conditions.Results show that different fragmentation patterns are possible according to initial particle size and heating severity. Under conditions typical of PF combustion, i.e. small particle size and very high temperature and heating rate, the main fragmentation pattern is exfoliation of the outer shell under the action of thermal shock which produces a multitude of fine particles. Under conditions typical of fixed/moving bed reactors, i.e. larger particles and lower temperature/heating rate, fragmentation occurs mainly at an inner radial position, close to the particle center, under the cooperative action of thermal stress and volatile overpressure, which produces a limited number of relatively coarse fragments. In some situations, such as for large particles and severe heating conditions, multiple successive events of exfoliation and fragmentation at the particle center are possible.

The fragmentation of coal particles during the coal combustion in a fluidized bed

This paper presents an experimental method for studying the fragmentation of coal particles during coal combustion in a fluidized bed and the quantitative fragmentation indexes of 10 typical Chinese coal ranks. The influences of a variety of factors such as the bed temperature, the size of coal particles, the coal rank and the fluidizing medium on the fragmentation index of coal particles are also studied. The research results show that the main reason for the fragmentation of coal particles is the primary fragmentation, and that the volatile matter can drastically influence the degree of fragmentation of coal particles.

98/00556 Fragmentation of coal particles at high temperature environment

98/00556 Fragmentation of coal particles at high temperature environment

97/02177 The research on the fragmentation of coal particles in a fluidized bed

This paper reports the determination of fragmentation of coal particles in a fluidized bed, and the quantitative index put forward to describe the fragmentation of coal particles in the fluidized bed. The influences of a variety of factors such as bed temperature, the time the coal stays in the fluidized bed, size of coal, coal rank and fluidizing medium on the index of the fragmentation of coal were studied at Zhejiang University. From the research results, one can draw a conclusion: the fragmentation of coal particles has different characteristics for varieties of coal ranks, and the main reasons for the fragmentation of coal particles are the first class fragmentation and the heat stress.