Effect Of Coal Particle Size Research Articles

Pyrolysis characteristics and product distribution of low-rank coal with heat-carrying particles adopting TG-FTIR and a novel self-mixing down tube reactor

A novel self-mixing down tube (SDT) pyrolyzer has been developed, which can separate the heat carrying particles preheated in the fluidized bed from the coal, and the two can be mixed through a specific structure to instantly heat the coal particles to a predetermined temperature. The present study investigated the pyrolysis behavior of low-rank coal with hot silica sand heat-carrying particles adopting TG-FTIR. Identifies optimal conditions for maximum tar production in a laboratory-scale SDT using a significantly larger range of coal feed rates (4 kg/h). An increase in the degree of coal metamorphism increased the initial temperature and the yield of char. The tar yield from Huolinhe lignite coal (6.56 %) and Daliuta bituminous coal (7.48 %) showing a trend of first increased and then decreased with elevating the operating temperature and optimal temperature at 520 °C, respectively. The effect of coal particle size on tar yield mainly comes from the different degrees of secondary cracking caused by contact with solid heat-carrying particles as well as the differences in the content of macerals. GC‒MS spectra of tar and deposited carbon on silica sand indicated that heavy tar can easily deposit on the surface of sand and form char through polymerization reactions.

Effect of Coal Particle Size on the Kinetics of Gas Hydrate Formation

Effect of Coal Particle Size on the Kinetics of Gas Hydrate Formation

Hygroscopicity of coal powders with different ranks

The hygroscopicity of coal powder is one of the crucial factors that determine its moisture content, which significantly affects its adhesion, flowability, charge properties, and combustion behavior. In this study, the effects of coal particle size, ambient temperature, and relative humidity on the hygroscopicity of coal powders with different ranks were investigated through experimental methods. The results indicated that an increase in coal particle size resulted in a moderate reduction in the maximum moisture adsorption capacity and a substantial increase in the effective moisture adsorption time of the coal powder. As the coal particle size increased from 19 to 21 μm to 6310–6941 μm, the maximum moisture adsorption capacities of the coal powders decreased by 0.28–0.54 times, while their effective moisture adsorption times increased by 1.47–1.68 times. The maximum moisture adsorption capacities of the coal powders increased dramatically with increasing ambient relative humidity, whereas the impact of temperature on their maximum moisture adsorption capacities was not significant. The hygroscopicity of coal powders varied significantly among different ranks. Low-rank coal such as lignite and subbituminous showed strong moisture adsorption ability, while high-rank coal such as anthracite exhibited moderate moisture adsorption ability, and middle-rank coal such as medium volatile bituminous showed the weakest moisture adsorption ability. FTIR spectra analysis and pore testing results revealed that the content of oxygen-containing functional groups and the distribution characteristics of internal pores were critical factors causing the difference in hygroscopicity of the coal powders. The practical value of this study lies in its potential to determine the moisture adsorption rate and the maximum moisture adsorption capacity of coal powder under specific environmental conditions, which is essential for evaluating the moisture status, transportation efficiency and combustion performance of coal powder.

The effect of adding tiny granules on the adsorption characteristics of granulated coal

ABSTRACT Water-based fracturing fluid is a key component in coal bed methane (CBM) extraction, which is a promising way forward for the green extraction of methane. The adsorption by coal is highly affected by tiny particles in the fracturing fluid. Aiming at exploring the effect of mixing non-adsorbent particles into coal on the adsorption, an atmospheric pressure granulated coal adsorption system with a flow meter was designed to perform tests. During the experiments, the effect of coal particle size, coal mass, and addition of tiny granules on adsorption was analyzed. The obtained results show that the addition of iron powder reduces the adsorption capacity and average adsorption rate of granular coal, and makes the adsorption speed peak earlier. It is found that the change in the adsorption amount has a weak positive correlation with the coal particle size, and the change of the average adsorption rate has a weak positive correlation with the size. However, in the absence of iron powder, the average adsorption rate is negatively correlated with the coal size, and the effect of the coal mass on the average adsorption rate and adsorption capacity is very weak. In large granular coal, the adsorption capacity is independent of size. Under the experimental conditions, strong adsorption occurred between 500 and 1750 s, and the adsorption kinetic process showed a slow-fast-slow “S”- curved distribution.

Computational Investigation on the Impact of Coal Feed Size in a Tangentially Fired Gasifier

ABSTRACT Using a validated comprehensive model, the effect of coal particle size on two-phase flow inside a tangentially fired, Mitsubishi Heavy Industry entrained-flow coal gasifier is investigated. It is observed that the length of the central recirculation zone (CRZ) formed in the gasifier flow increases with an increase in the mean size of the injected coal particles. The CRZ lengths are 5.6, 4.5 & 2.1 m, respectively, for the cases with particle size distributions (PSDs) having mass mean diameters of 80, 40 & 20 µm. The generic swirl number, , captures this impact of particle size on the CRZ length, whereas the conventional swirl number, , is unable to do so. The value of does not vary significantly over most of the gasifier’s constant diameter zone in each case simulated in the present work, thereby underlining the utility of this swirl number to characterize similarity in swirl dynamics. Further, the analysis of the impact of coal particle size on char conversion yields that the PSD with finer particles leads to higher conversion due to the better combustibility of finer particles.

Effect of Coal Particle Size on Dilatation

Effect of Coal Particle Size on Dilatation

Effective thermal conductivity of loose residual coal in goaf: Comparative analysis of experiment and model

The effective thermal conductivity (ETC) model of loose residual coal in goaf is a method to study the heat transfer law of spontaneous combustion in goaf. In order to study the effect of coal particle size and ambient temperature on heat transfer, coal samples of different sizes were taken from the FuSheng (FS) mine, and the void fraction, the thermal conductivity (TC) of the residual coal under different ambient temperature were tested. Additionally, four types of ETC models of loose residual coal in goaf were obtained and the average relative errors of the TC were analyzed. The results showed that the void fraction, the coal particle size and ambient temperature have different effects on the spontaneous combustion of the residual coal. The effect of coal sample size on the heat transfer is 100 times that of the ambient temperature. The changes in the ETC and average relative error of the different models were consistent. The heat transfer in the spontaneous combustion of residual coal has a direct relationship with the spatial distribution and heat transfer modes of the loose residual coal in the goaf.

Coal Moisture Variations in Response to Rainfall Event in Mines and Coal-Fired Power Plant Stockpiles—Part 1: Runoff, Infiltration, and Drainage

Excessive coal moisture leads to a lower heating value and power plant efficiency, and increased transportation costs. Therefore, coal stockpile management and moisture control are particularly important in regions with heavy precipitation. This paper and Part 2 address factors influencing moisture retention and migration in coal stockpiles. Part 1 of this paper series simulates phenomena of runoff, infiltration, and drainage in a stockpile after a rainfall event. Part 2 reports the effect of coal particle size and climate conditions on the rate and depth of moisture evaporation process within a coal stockpile. To perform this study, two coal samples were collected from the Witbank mine in South Africa. The results of the present study showed that smaller interparticulate void spaces because of the compaction or fines particles (−0.5 mm fraction) inhibited infiltration, leading to increased runoff volume. An increase stockpile slope increased the amount of runoff due to coal–water contact time reduction. The ability of heavy rainfall to destroy near-surface structures (erosion) happened more readily at stockpiles with high slopes and high fine content. The fine content significantly influenced the dewatering efficiency of drainage. Coals with higher ash contents had stronger moisture retention ability than that of other coals even though coals with low ash contents had a high fine content. This was ascribed to the contribution of the clay minerals, such as kaolinite, in the high ash coal. The results of this paper can be used for the effective management of coal stockpiles to prevent excessive moisture in stockpiles for the best possible utilisation of coal in power plants.

Experimental Study on the Effect of Coal Particle Size on the Mechanics, Pore Structure, and Permeability of Coal-like Materials for Low-Rank Coalbed Methane Reservoir Simulation

Coal-like materials have been widely used to simulate low-rank coalbed methane (CBM) reservoirs to develop fracturing stimulation technology since the transportation and preparation of low-rank coal produce easily secondary damages, causing large dispersion of test results. However, the coal particle sizes have a significant effect on the performance of coal-like materials among many factors. Hence, to accurately simulate low-rank CBM reservoirs for promoting the development of reservoir stimulation technologies, cement, gypsum, pulverized coal, and sand were selected as similar materials to make coal-like samples with different coal particle sizes to study the influence law of coal particle size on the mechanics, pore structure, and permeability of samples. The ultrasonic wave velocity, dynamic parameters, uniaxial compressive strength, elastic modulus, and uniaxial tensile strength of samples increased with increasing coal particle size in the range of 0–2 mm. However, these parameters suddenly decreased when the coal particle size increased to 2–3 mm. The porosity and permeability of the samples exhibited an opposite trend compared to the above parameters. The fracture occurred in cementing materials, and the crack extension direction was affected by the coal particle sizes. The fracture complexity of the coal-like samples decreased with increasing particle size under uniaxial compressive testing. The failure mode was mainly a tensile failure, supplemented by shear failure. The coal-like materials can well meet the performance requirements of low-rank CBM reservoirs.

Investigating the effect of coal particle size on spontaneous combustion and oxidation characteristics of coal.

As a key parameter, the particle size of residual coal contributes greatly to its oxidation characteristics, so it is a significant and far-reaching topic to explore the role of different particle sizes in coal spontaneous combustion disaster. In this work, temperature-programmed system (TPS) was applied to analyze the oxygen consumption rate and CO and C2H4 production rules of six groups of coal samples with different particle sizes in the process of oxidation heating. The critical temperature (CT) and xerochasy temperature (XT) of different coal samples were obtained, and the coal oxidation process was divided into three stages (S1, slow oxidation stage; S2, fast oxidation stage; and S3, combustion stage). Then, the apparent activation energy (E) and pre-exponential factor (A) in three stages were regressed combined with Arrhenius formula. The results show that the smaller the coal particle size is, the larger the specific surface area is, the stronger the adsorption capacity of coal molecules and oxygen molecules is, resulting in the larger oxygen consumption rate. The values of CT and XT with particle size of 0.125-0.18mm and 2-4mm are the smallest and largest. For coal samples with the same particle size, the maximum values of E and A occur in stage S3 and the minimum values appear in stage S1. This is mainly due to the higher temperature of stage S3, which allows the activation of functional groups with higher apparent activation energy, stronger collisions between activated molecules, and more intense oxidation reactions.

Effects of coal particle size on the two-phase flow and slagging performance in a swirl burner

Swirl burner is widely used in coal-fired boilers. Coal particle size is an important factor affecting the two-phase flow as well as the combustion performances of a swirl burner. A bench-scale experiment with CFD simulation was conducted with full burner complexity. The results show that asymmetry of the particle phase is gradually weakened as the particle size increases, opposite to the variation trend of the continuous flow field in a hot state. The asymmetry of the particle phase is much more affected by the asymmetry of the secondary air jet flow than that of the primary air jet flow. As the particle size increases within a certain range, the combustibility of pulverized coal decreases, which enhances the asymmetry of the continuous flow field. When the particle size increases more than 50 μm, an increase in the concentration of incomplete combustion particles in the side recirculation zone around the burner occurs, intensifying the tendency of slagging. Thus, controlling the pulverized coal particle size below 50 μm is a considerable choice to improve combustion efficiency and avoid slagging.

Effect of coal particle size on gasification performance of two‐stage entrained‐flow coal gasifier

AbstractTo clarify the effect of coal particle sizes on gasification performance of an advanced two‐stage entrained‐flow coal gasifier for IGCC (integrated gasification combined cycle) application, a comprehensive three‐dimensional numerical model is established by incorporating the shrinking core model combined with the Langmuir‐Hinshelwood kinetic rate expression, which considers the inhibitory effect of CO on char‐CO2 reaction. The flow, temperature, and species distributions were obtained, and the results are consistent with the operating data. Results show that the helical flow and eight recirculation zones in the gasifier improve carbon conversion efficiency through extending the residence time of coal particles. Slow devolatilization of large particles caused by slow heating retards volatiles combustion, and thus char combustion and gasification. As a result, less char gasification and higher gas temperature appear in the injection region of the first stage. Higher inertia of larger particles produces higher slip velocity, which enhances heat transfer and mass diffusion to char particles and increases char consumption rate in diffusion‐limited regions. The regions of high inner wall temperature spread from locations around burners to the whole inner wall of the injection and bottom regions in the first stage with increase of coal particle sizes.

Study on the evolution of internal and external water of lignite during microwave drying and the moisture reabsorption characteristics of dried lignite

ABSTRACT Lignite with high moisture content needs to be dried. The variations of internal and external water of Mindong lignite during microwave drying were studied. The effects of coal particle size (<0.2 mm, 1–4 mm, 8–12 mm) and target moisture content (20%, 15%, 10%) on the moisture re-absorption characteristics of dried samples were analyzed. It was found that microwave heating quickly removes the moisture of lignite, showing an exceptionally positive effect on the removal of internal water. During the drying process, the pore volume of lignite first decreases and then increases, while the content of oxygen-containing functional groups such as hydroxyl and carboxyl group on the surface of lignite decreases. When dried lignite is under a normal atmosphere, lower moisture content and smaller particle size lead to more water to be reabsorbed; The external water contents of coal samples (8–12 mm) with target moisture content of 20%, 15% and 10% are 5.45%, 5.44% and 5.21%, respectively, which shows the similar external water content. The experimental results are conducive to exploring the moisture migration path during drying and re-absorption of dried lignite. Considering the balance of drying and re-absorption, microwave drying of lignite should have optimum target moisture contents and material particle sizes, depending on the specific conditions and requirements. The research provides theoretical guidance for the industrial application of lignite drying.

Computational Study of 16 kWth Furnace Cofired Using Pulverized Bituminous Coal and Liquified Petroleum Gas Operated in Un-Staged and Air-Staged Conditions

Abstract This paper presents a computational study on air-fuel combustion of bituminous coal and liquified petroleum gas (LPG) in a 16 kWth test facility with a coflow-swirl burner. The performance of three turbulence models is investigated for the furnace operated under both air-staged and un-staged conditions by comparing their predictions with the reported measurements of temperature and species concentrations. This comparison shows that the shear stress transport (SST) k–ω model and SST k–ω model with low-Re correction predict the profiles of temperature and species concentrations reasonably well, but significantly underpredict the temperature in the furnace core at axial locations away from the burner. On the other hand, the transition SST k–ω model provides better overall congruency with the measured temperature and species concentrations when compared with the other turbulence models used, as indicated by relatively higher values of the Pearson correlation coefficient at locations away from the burner. The present high-fidelity computational model developed is also capable of accurately simulating the effect of coal particle size on the furnace environment, which is verified by the match between the computational predictions and the experimental results for two different sized coal samples. The model is also used to investigate the effect of coal particle size on the internal recirculation zone (IRZ) and the reattachment length (LR) for the same inlet swirl number (SN). A decrease of nearly 50% in the coal sample size results in the increase of LR and IRZ length by 20% and 82.6%, respectively.

Process intensification on suspension pyrolysis of ultra-fine low-rank pulverized coal via conveyor bed on pilot scale: Distribution and characteristics of products

From the perspective of intensifying the pyrolysis process, suspension pyrolysis characteristics of ultra-fine low-rank coal via conveyor bed (1500 kg/h) were studied. The effects of coal particle size, pyrolysis temperature, and heating rates on the distribution of products were investigated. The relationship between the pyrolysis process and product quality, such as gas, tar, and char, was analyzed. The results showed that suspension pyrolysis enhanced the heat and mass transfer of the upgrading process. When the pyrolysis temperature was between 550 and 650 °C and coal particle size in the range of 0.075 ~ 0.105 mm, the yield of tar reached about 145% of the Gray-King tar yield. The analysis of group composition and four main components of tar showed that each fraction contained a certain amount of chain hydrocarbons or saturated hydrocarbons, which were mainly aromatic hydrocarbon compounds. The effective gas content from pyrolysis was H2 (19.32 vol%), CH4 (17.59 vol%), CO (12.53 vol%), and the low calorific value was about 900 kcal/Nm3. With the increase of pyrolysis temperature, the overall yield of pyrolysis gas increased, and the yields of H2 and CH4 increased linearly with temperature. The mass fraction of volatiles in char was less than 8%, while the mass content of fixed carbon was more than 80%. With the increase of pyrolysis temperature, the fixed carbon and ash content of the char increased, but the volatile matter decreased. This study provides a fundamental basis for the improvement of the pulverized coal pyrolysis process on large-scale installation.

Investigation of thermochemical process of coal particle packed bed reactions for the development of UCG

In this study, a packed bed reactor was developed to investigate the gasification process of coal particles. The effects of coal particle size and heater temperature of reactor were examined to identify the thermochemical processes through the packed bed. Three different coal samples with varying size, named as A, B, and C, are used, and the experimental results show that the packed bed with smaller coal size has higher temperature, reaching 624 °C, 582 °C, and 569 °C for coal A, B, and C, respectively. In the case of CO formation, the smaller particle size has greater products in the unit of mole fraction over the area of generation. However, the variation in the porosity of the packed bed due to different coal particle sizes affects the reactions through the oxygen access. Consequently, the CO formation is least from the coal packed bed formed by the smallest particle size A. A second test with the temperature variations shows that the higher heater temperature promotes the chemical reactions, resulting in the increased gas products. The findings indicate the important role of coal seam porosity in underground coal gasification application, as well as temperature to promote the syngas productions.

Gasification of Shenhua Bituminous Coal with CO2: Effect of Coal Particle Size on Kinetic Behavior and Ash Fusibility

Coal gasification is the process that produces valuable gaseous mixtures consisting primarily of H2 and CO, which can be used to produce liquid fuel and various kinds of chemicals. The literature shows that the effect of particle size on coal gasification and fusibility of coal ash is not clear. In this study, the gasification kinetics and ash fusibility of three coal samples with different particle size ranges were investigated. Thermogravimetric results of coal under a CO2 atmosphere showed that the whole weight loss process consisted of three stages: the loss of moisture, the release of volatile matter, and char gasification with CO2. Coal is a heterogeneous material containing impurities. Different grinding fineness leads to different liberation degrees for impurities. As for the effect of particle size on TG (thermogravimetry) curves, we found that the final solid residue amount was the largest for the coal sample with the smallest particle size. The Miura-Maki isoconversional model was proved to be appropriate to estimate the activation energy and its value experienced a slow increase when the particle size of raw coal increased. Further, we found that particle size had an important impact on ash fusion temperatures and small particle size resulted in higher ash fusion temperatures.

Experimental study on the effects of coal particle size and fissure size on underground coal fires

Underground coal fire (UCF) widely spreads in many countries, which is a serious threat to the environment and the safety of coal mining industries. The cause of UCF is complex and affected by many factors such as fissures and coal seam porosity. For the first time, a novel experimental framework is proposed to simulate UCF. Two variables i.e., the coal particle size (6mm, 9mm and 15mm) and fissure size (1cm, 2cm, 4cm and 6cm) are considered in experiments. The peak temperature, air velocity and the propagation rates of dry front, pyrolysis front and oxidation front are analyzed. The results show that peak temperature and spread rate of UCF increase if the particle size or fissure size increase. In the smoldering stage, the ventilation is driven by buoyancy force produced by hot smoke. And this driving action increases with the particle size or fissure size, which further promotes smoldering by inhaling more air. The smoldering may turn to flaming combustion when the particle size is 9mm with fissure size ⩾ 4cm or the particle size is 15mm.

Effect of Particle Sizes on the Physical and Mechanical Properties of Briquettes

The particle size of coal particles is an important factor affecting the physical and mechanical properties of coal. In this study, uniaxial and triaxial compression tests were conducted to investigate the effects of coal particle size on the physical and mechanical properties of briquettes and their impact mechanism using a rock mechanics test-150B servo system (RMT-150B). The results showed that the uniaxial compression strength, elastic modulus and deformation modulus of briquettes increase when particle size is decreased. The deformation characteristics of the briquettes directly prepared by raw tectonic coal were similar to those of coal specimens with a particle size of 0.18–0.25 mm. The cohesion and strength of coal specimens increased when particle size was decreased, and the plastic deformation capacity decreased when particle size was decreased, showing a strong correlation. The f briquette directly prepared by the raw tectonic coal had a strength between that of coal specimens with a particle size of 2–6 mm and those with a particle size of 0.18–0.25 mm. The mechanical properties of briquettes mainly depend on the meshing force between the coal particles. The smaller the particles, the greater the mechanical meshing force. The “floating particles”, generated in the voids between coal particles during the preparation process, are a significant factor affecting the plasticity characteristics. The research results may be used as a basic reference in the study of the mechanical properties of tectonic coal, gas migration and coal and gas outburst mechanisms.

Evaluation of coal conversion pathways in fluidized bed chemical looping combustion with oxygen uncoupling (CLOU)

Chemical looping with oxygen uncoupling (CLOU) is a variant of chemical looping combustion that uses oxygen carriers that release gaseous O2 in the fuel reactor to efficiently combust solid char. There are many different pathways by which fuel carbon can be converted in a CLOU system, including reaction of volatiles, oxidation of char and gasification of char followed by conversion of the gaseous products. Therefore, there is competition between volatiles and solid char for both gaseous and metal bound oxygen. This study presents an experimental method of analysis to better understand the conversion pathway and fate of fuel carbon in a fluidized bed reactor system. The analysis is applied to a Cu-based CLOU carrier in a bench-scale reactor, feeding either coal or coal char in small batches. The effect of coal particle size and reactor temperature on the relative contributions of different carbon conversion pathways is evaluated. Under the conditions studied, higher temperatures and smaller char particles were more effectively converted by gaseous O2 released by the CLOU carrier, resulting in less unconverted char. However, there was more unconverted volatiles exiting the reactor from small coal particles and the resulting char had a higher tendency to exit the fuel reactor unconverted. Larger char particles relied more on conversion by gasification and subsequent oxidation of combustible products. Results for other systems will depend on operating conditions and properties of the fuel, but conversion pathways can be systematically evaluated using the method described.