Coal Particle Diameter Research Articles

Analysis of influencing factors in permittivity of oxidized lignite by FTIR, XRD, and THz-TDS based on orthogonal experiment

As an organic-rich and mineral-rich mixture, the permittivity of oxidized lignite is dependent on several factors in the terahertz (THz) band. In this study, thermogravimetric experiments were conducted to determine the characteristic temperatures of three types of lignite. The microstructural characteristics of lignite after treatment at 150, 300, and 450 °C were investigated by Fourier transform infrared spectroscopy and X-ray diffraction. The results show that the changes in the relative contents of CO and SiO are contrary to those of OH and CH3/CH2 with temperature variation. The relative content of CO is unpredictable at 300 °C. The aromaticity and crystallite diameter show a regular variation with temperature. The microcrystalline structure of coal tends to undergo graphitization with temperature. The variation of crystallite height is random at 450 °C. The uniform variation in microstructural characteristics of different types of lignite with oxidation temperature proves the feasibility of identifying oxidized lignite by THz spectroscopy. Based on orthogonal experiment results, the influence of the coal type, particle diameter, oxidation temperature, and moisture content on the permittivity of oxidized lignite in the THz band was arranged in an order. The order of the factors’ sensitivity for real part of permittivity is oxidation temperature > moisture content > coal type > particle diameter. Similarly, the order of the factors’ sensitivity for imaginary part of permittivity is oxidation temperature > moisture content > particle diameter > coal type. The results reveal the capability of THz technology to characterize the microstructure of oxidized lignite and provide guidance for minimizing error in THz technology.

Stamp-Charged Coke-Making Technology—An Empirical Model for Prediction of Coal Charge Density for Stamp Charging Coke Oven Batteries

Coke-making technology utilises two systems for charging the coke oven chambers with coal—a stamp-charged system (stamp-charging) and a gravity charged system (top charging). The presented study examines the impact of selected coal properties on the effectivity of the stamping operation by measuring the bulk density of the obtained stamped coal cake. An empirical mathematical model was developed that allows the forecasting of the coal cake density based on the most frequently assessed coal parameters, such as volatile matter, ash, moisture and particle size parameters, as well as the stamping operation parameter—cumulative stamping energy. The obtained results showed that the density of the stamped coal cake increases with the increase in the stamping energy (53.3 kg/m3 increase, for increase in natural logarithm value of 1), RRSB specific coal particle diameter d′ (6.4 kg/m3 increase, for each 0.1 mm increase in d′), ash content (8.9 kg/m3 increase, for 1% point increase) and moisture content (4 kg/m3 increase, for 1% point increase), and decreases with the increase in volatile matter content (3.82 kg/m3 decrease, for 1% point increase).

Experimental research on desorption characteristics of gas-bearing coal subjected to mechanical vibration

Mechanical vibration can induce coal and gas outburst accidents, and can also promote the exploitation of coalbed methane. In this paper, a vibration-adsorption-desorption experiment system was established, the effects of coal sample particle diameter, gas pressure, and vibration frequency on gas desorption were studied. Mechanical vibration can generate a shear force in the adsorbed gas and promote gas desorption, but there are appropriate vibration parameters. Within the range of experimental parameters, the larger the amplitude, the more favorable for gas desorption. The change rules of gas desorption rate and desorption quantity under different conditions are basically the same, showing a power function shape with time increase, and most of the desorption quantity was completed within the first 5 minutes. The gas desorption rate and desorption quantity were positively related to the gas adsorption pressure. The results have great reference value for preventing gas outbursts and promoting gas exploitation.

Modeling of single coal particle combustion in O2/N2 and O2/CO2 atmospheres under fluidized bed condition

A one-dimensional transient single coal particle combustion model was proposed to investigate the characteristics of single coal particle combustion in both O2/N2 and O2/CO2 atmospheres under the fluidized bed combustion condition. The model accounted for the fuel devolatilization, moisture evaporation, heterogeneous reaction as well as homogeneous reactions integrated with the heat and mass transfer from the fluidized bed environment to the coal particle. This model was validated by comparing the model prediction with the experimental results in the literature, and a satisfactory agreement between modeling and experiments proved the reliability of the model. The modeling results demonstrated that the carbon conversion rate of a single coal particle (diameter 6 to 8 mm) under fluidized bed conditions (bed temperature 1088 K) in an O2/CO2 (30:70) atmosphere was promoted by the gasification reaction, which was considerably greater than that in the O2/N2 (30:70) atmosphere. In addition, the surface and center temperatures of the particle evolved similarly, no matter it is under the O2/N2 condition or the O2/CO2 condition. A further analysis indicated that similar trends of the temperature evolution under different atmospheres were caused by the fact that the strong heat transfer under the fluidized bed condition overwhelmingly dominated the temperature evolution rather than the heat release of the chemical reaction.

Hybrid Flamelet/Progress Variable Approach for NO Prediction in Pulverized Coal Flames

The flamelet/progress variable (FPV) approach is further extended for a better prediction of NO emission in pulverized coal flames. The predicted results are compared with detailed chemistry simulation solutions for model evaluation. The results show that the original FPV approach with a conventional progress variable consisting of major species can predict the gas temperature and major products well but can roughly predict the NO variation. Therefore, the extended FPV approach with a modified progress variable including both NO and major species is further evaluated. The results indicate that the prediction accuracy of NO is sensitive to the proportion of NO introduced in the modified progress variable. The best prediction of NO can be obtained with the modified progress variable where the concentration of NO is comparable to that of all major species. However, the predictions of other quantities of interest are simultaneously deteriorated to some extent. Based on these analyses, a hybrid FPV approach is developed in which two flamelet libraries are constructed with conventional and modified progress variables, respectively. The results indicate that the hybrid FPV approach can predict both NO and other quantities of interest quite well at the same time under various operating conditions of strain rate, coal particle diameter, coal mass flow rate, and initial temperature.

Discharge flow and dynamic stress of coal particles in rectangular silos with pyramidal hopper

ABSTRACT To study the particle discharge flow and dynamic stresses in silos, an overhead rectangular silo with pyramidal hopper was designed and tested. The inclination of the discharge hopper and the size of the rectangular cross-section are adjustable. Based on inclinations of 45°, 55°, 65° for the pyramidal hopper, nine groups of discharge flow experiments were performed by using coal particle diameters of < 3 mm, 3–6 mm, and 3–13 mm. The results showed that the smaller dry coal particles performed better; furthermore, the height-to-diameter ratio of the straight silo and the inclination of the discharge hopper affected the flow of coal particles. The distribution of the dynamic side stress in the middle silo plate during discharge was indirectly tested. The results showed that the maximum stress appeared around the middle of the straight silo. During discharge, the lateral stresses in the silos were larger than the static stresses, with obvious overstresses in the middle and upper parts of the silos. Decompression was observed in the hopper.

Numerical study of a large-scale pulverized coal-fired boiler operation using CFD modeling based on the probability density function method

The paper presents results of numerical modeling of pulverized coal combustion process in the front wall coal-fired boiler. The developed numerical model of the coal combustion process included particle heating, devolatilization, char combustion, as well as turbulent flow and radiative heat transfer. In gas phase combustion process modeling, the mixture fraction approach with PDF was used. Presented modeling results were carried out using the Open Source CFD code – Code_Saturne, and were used to study the pulverized coal combustion in a 225 MWe power plant unit. The input data and boundary conditions were defined based on the collected data about boiler operating conditions and Rosin-Rammler law was used to calculate coal particle distribution. The behavior of pulverized coal and air flow through the burners, as well as the three-dimensional flue gas path through the combustion chamber, was analyzed. Results in form of velocity, temperature, unburned coal and combustion products distribution were presented to show places inside the boiler with high erosion hazard and place where intensive particle deposition may occur, as well as to show the impact of coal particle diameters on Unburned Carbon (UBC) content. Calculation results confirm proper locations of Over-Fire Air (OFA) nozzles and allowing continuing of combustion process at the furnace outlet using only OFA II and OFA III nozzles set. Based on the obtained results is possible to increase the understanding and conduction detailed investigation of boiler operation. The results have been validated with data collected from the power station measurement system and were analyzed in order to find an answer for operational questions regarding optimization of combustion characteristics.

Prediction of product distributions in coal devolatilization by an artificial neural network model

Currently most coal combustion simulations treat the devolatilization products as a mixture of light gases with a given proportion or a postulate substance, which is obviously different from the reality. To obtain a more accurate treatment on the product distribution from coal devolatilization, an artificial neural network (ANN) model is innovatively developed based on a training database constructed from diverse experimental data for a wide range of coal types under a wide range of heating conditions. The accuracy and applicability of the developed ANN model are validated and compared with that of the chemical percolation devolatilization coupled with the functional group (FG-CPD) model for the validation database, and the relative impact of each input parameter on the evolution of each devolatilization product is evaluated. The results show that the detailed product distributions of coal devolatilization predicted by the proposed ANN model are in good agreement with the experimental data for both the training and validation database, and the ANN model can give a more accurate prediction on both the yield of each component and its evolution compared with the FG-CPD model. The coal composition accounts for the most impact (above 60%) on the product distribution, and the relative impact of Cdaf, Hdaf, Odaf, coal particle diameter, instantaneous heating rates, particle residence time and particle temperature decrease successively. This ANN model has great potential to be coupled into coal combustion simulations to improve efficiency and accuracy, which will be studied in the future.

Determining the Interactive Effects in CO2 Capture Integrated with Coal Flotation by High-Order Multifield Synergy Model

CO capture is very essential to mitigate the greenhouse gas control. However, the CO desorption is quite costly during CO capture. To reduce the cost, the CO desorption integrated with coal flotation was developed as a retrofitted process, which can simultaneously achieve the CO desorption and coal flotation. To determine the key interactive effects between coal, amine, and CO in the process, a high-order multifield synergy model was developed accordingly. According to the high-order multifield synergy model, the effects of coal particle diameter, coal weight fraction, CO loading, and amine on the CO desorption and coal flotation were analyzed in detail. It was found that there is almost twice the CO amount at coal weight fraction of 0.06 than that at a coal weight fraction of 0.02. The coal recovery rate at 0.35 mol/mol is twice of that at 0.15 mol/mol. The adsorption energy, adsorption layer thickness, and zeta potential determine the interactive effects between coal, amine, and CO. The coal, amine, and CO system increases the coal recovery rate by 25% and reduces the CO desorption energy by 20% with desorption temperature below 373 K. The high-order multifield synergy model shows the advantages of higher prediction accuracy and is easier to converge than the conventional multifield synergy model.

Devolatilization and Combustion of Coarse-Sized Coal Particles in Oxy–Fuel Conditions: Experimental and Modeling Studies

A generalized unsteady-state kinetic model, coupled with all modes of heat transfer, was developed to describe the combined coal devolatilization and the subsequent combustion of the residual char under oxy–fuel condition in both O2–CO2 and O2–N2 environments. Experiments were conducted to validate the model, which was also found to predict the experimental data published in the literature well. The effect of coal particle diameter, temperature of the reactor, and oxygen concentration on devolatilization time was investigated. Peaks in devolatilization and char combustion rates and particle center temperature were studied, and the effect of different parameters assessed. Higher reaction time was observed in an O2–CO2 environment compared to that in an O2–N2 environment due to lower particle temperatures resulting from endothermic gasification reaction and the difference in thermo-physical properties. Simulation studies were carried out to generate temperature, carbon, O2, CO, and CO2 contours to understan...

Investigation of heat and mass transfer processes in the combustion chambe of industrial power plant boiler. Part 2. Distribution of concentrations of O2, CO, CO2, NO

In the present paper, a study of furnace processes in the combustion chamber of the real energy boiler BKZ-160 of Almaty TPP-3 (Kazakhstan) using three-dimensional modeling methods has been carried out. Calculations of the combustion chamber for flame combustion of pulverized coal have been performed. The main purpose of this paper was to study the effect of fractional fuel composition on the concentration characteristics of the combustion process. Numerical simulation was carried out with two models of coal particle size distribution: monodisperse fuel flame (coal particle size identical and equal to 60 μm) and a polydisperse fuel flame (coal particle diameter varies from 10 to 120 μm). The polydisperse distribution corresponds to the fractional distribution (percentage of total coal particles) calculated for this boiler: the first fraction - 10% with d p =10 μm; 20% with d p =30 μm; 40% with d p =60 μm; 20% with d p =100 μm; 10% with d p =120 μm.The numerical simulation results of the influence of the pulverized coal particle size composition on concentration characteristics of combustion process are presented. The distributions of oxidizer (oxygen) and combustion products (NO, CO, CO 2 ) are shown. Areas with the greatest concentration of gas products of burning are determined, regularities of formation of products and their concentration at the exit of fire chamber are also determined. The effect of fractional fuel composition on the obtained characteristics is sufficiently large, the empirical data obtained directly at TPP-3 show better convergence with the result of the computational experiment that confirms simultaneously the adequacy of the used physical and mathematical statement of the problem, as well as the validity of using the model of polyfractional distribution.

Fragmentation model of coal devolatilisation in fluidised bed combustion

ABSTRACTDevolatilisation is the release of volatile compounds from coal matrix by thermal decomposition. During coal devolatilisation, fragmentation could occur due to pressure build-up of accumulated volatiles. A fragmentation model is necessary to ensure the safe operation of coal combustion and optimum process condition. In this study, the refinement of fragmentation model of coal devolatilisation was done. In order to obtain a comprehensive model, a fluidised bed combustion experiment was conducted using two Indonesian coals (Musi Banyuasin and Berau) and the results were then compared with the model simulation. Using a coal diameter of 0.8–17 mm at a combustion temperature of 850°C, it shows that the fragmentation probability and number of fragments could be affected by the coal particle diameter, convective pore diameter, and porosity. Predictions made by the developed model were close to the experimental fragmentation data, with an error range of less than 5.1%.

Numerical simulation and cold experimental research of a low-NOx combustion technology for pulverized low-volatile coal

Large quantities of low-volatile coal are utilized in power plants throughout China. With increasingly stringent environmental regulations, it is important to develop and deploy low-NOx combustion technologies for pulverized coal boilers burning low-volatile coal. The objective of this study was to investigate a novel decoupling combustion system for low-volatile coal via experiments and computational fluid dynamics (CFD). The combustion system includes horizontal fuel-rich/lean low-NOx burners (LNB) and the associated air distribution system for a polygonal tangentially fired boiler (PTFB). The effects of coal particle diameter and coal feeding rate on the gas/particle flow characteristics of the burner, and the cold state aerodynamic field of the PTFB were analyzed in detail. The structural design of the LNB results in advantageous gas/particle flow characteristics and the PTFB improved the distribution of the flow field. The CFD models and simulation results were validated by comparing with those of cold experiments data. The simulation results demonstrated that this low-NOx combustion technology enhances staged combustion at different scales, which can reduce NOx generation significantly. In the industrial application on a 300MW pulverized coal boiler, installation of the LNBs improved the stability of low-volatile coal combustion and reduced NOx emissions significantly. These research findings provide valuable guidance to the design of low-NOx combustion system for pulverized coal boilers using low volatile coal.

Nonintrusive Uncertainty Quantification of Computational Fluid Dynamics Simulations of a Bench-Scale Fluidized-Bed Gasifier

Uncertainty quantification (UQ) analysis is increasingly becoming one of the major requirements of simulation-based engineering to assess the confidence in the results and make better-informed decisions based on the insight derived from the simulations. In an earlier study, Bayesian UQ analysis was applied to existing bench-scale fluidized-bed gasifier experiment results. In the current study, a series of simulations were carried over with the open-source computational fluid dynamics software MFiX to reproduce the experimental conditions, where three operating factors, i.e., coal flow rate, coal particle diameter, and steam-to-oxygen ratio, were systematically varied to understand their effect on the syngas composition. Bayesian UQ analysis was this time performed on the numerical results for comparison purposes. This is part of ongoing research efforts to explore the applicability of advanced UQ methods and processes such as Bayesian methods for large-scale complex multiphase flow simulations. As part of Bayesian UQ analysis, a global sensitivity analysis was performed based on the simulation results, which shows that the predicted syngas composition is strongly affected not only by the steam-to-oxygen ratio (which was observed in experiments as well) but also by variation in the coal flow rate and particle diameter (which was not observed in experiments). The carbon monoxide mole fraction is underpredicted at lower steam-to-oxygen ratios and overpredicted at higher steam-to-oxygen ratios. The opposite trend is observed for the carbon dioxide mole fraction. These discrepancies are attributed to either excessive segregation of the phases that leads to the fuel-rich or -lean regions or alternatively the selection of reaction models, where different reaction models and kinetics can lead to different syngas compositions throughout the gasifier.

A DNS study on effect of coal particle swelling due to devolatilization on pulverized coal jet flame

The effects of particle swelling and shrinkage during devolatilization and char combustion on the flame characteristics are investigated by performing DNS of a lab-scale turbulent pulverized-coal straight-jet flame. The obtained characteristics are compared with those in the previous DNS (Hara et al., 2015), in which particle swelling and shrinkage are not taken into account. The results show that the changes in coal-particle diameter because of swelling and shrinkage during devolatilization and char combustion do not affect significantly the gas temperature distribution of the turbulent pulverized-coal straight-jet flame, although it explicitly affects the coal-particle diameter distribution in the flame.

Theoretical analysis of coal stockpile self-heating

This paper theoretically analyses the problem of coal stockpile self-heating under free convection (no wind) conditions. Scale analysis has been used to drive expressions for the stockpile temperature and inflection point (when the stockpile is completely dry) as functions of the key parameters including the coal type, moisture content, and particle diameter as well as the ambient air temperature. Theoretical predictions are then successfully compared with experimental data and CFD simulations results available in the open literature.

SO2 removal with coal slurry in a double-stirred vessel

In the coal slurry scrubbing process, SO2 can be removed through both the coal pyrite leaching reaction and the oxidation reactions catalysed by Fe2+/Fe3+ produced in situ. In the present study, experiments of SO2 removal with coal slurry (particle size fraction 65–150 μm) were carried out using a double-stirred vessel to investigate the effects of temperature, coal particle size and pulp density on SO2 absorption rate and on the proportion of SO2 removed through the leaching reaction. Results show that the SO2 absorption rate can be increased by decreasing particle size and increasing pulp density, but it is relatively less affected by temperature. Although decreasing coal particle size and pulp density can increase coal pyrite conversion, the effectiveness is limited and the proportion of SO2 removed through the leaching reaction is little affected. Increasing temperature can evidently increase the proportion, but there also exists the problem of energy expenditure; satisfactory coal pyrite conversion during SO2 removal could not be achieved economically by such measures. In addition, the apparent rate constant has a linear relationship with the reciprocal of the coal particle diameter.

Study on Factors Influencing Pulverized Coal Ignition Time

Pulverized coal ignition time is one of crucial parameters in coal ignition process. Based on a general heat absorption equation without chemical reaction, this study was focused on some crucial factors which influence pulverized coal ignition time to theoretically explain the mechanism of heat absorption of pulverized coal. The influences of recirculated flue gas (RFG) temperature, flame temperature, primary air temperature, and coal particle diameter on ignition time were discussed. The importance of radiation heat and convection heat was analyzed. The results show that the higher temperatures of RFG, flame, and primary air can lead to the shorter ignition time respectively. The increase of the coal particle diameter greatly increases the ignition time, and as the diameter goes up, the amount of the ignition delay becomes greater. For high accuracy of ignition time calculation, both radiation heat and convection heat should be taken into account. When flame temperature is very high and RFG temperature is very low, radiation is the dominant factor, otherwise convection is more crucial.

Numerical investigation of the effect of the heterogeneous reaction model on the thermal behavior of pulverized coal combustion

ABSTRACTTo achieve high efficiency in pulverized coal combustion furnace and burner, the detailed estimation of the burn‐off time and thermal behavior of pulverized coal particles is important. The volume reaction and unreacted core models have been employed as solid–gas reaction model for a pulverized coal particle. Moreover, the possibility that the heat of reaction generated on the particle surface does not fully contribute as heating source to the coal particle should be considered. In this study, the heat and mass transfer around a single pulverized coal char particle exposed to a simplified heating environment are numerically analyzed to investigate the influence of the different coal ranks in their reactivity, coal char particle diameter, and reaction models for the burn‐off time and thermal behavior of the pulverized coal particle. From the sensitivity analysis of the reaction models for the burn‐off time, the importance of model selection when dealing the coal char particle with high reaction rates is indicated. © 2012 Curtin University of Technology and John Wiley &amp; Sons, Ltd.

Prediction of lean flammability limit and flame propagation velocity for oxy-fuel fired pulverized coal combustion

Lean flammability limit and flame propagation velocity are fundamental properties for engineering design of combustion systems. We developed a model to predict these properties for oxy-fuel fired pulverized coal combustion systems. We measured relationships between lean flammability limit and flame propagation velocity for various coal properties, particle diameter, composition of combustion supporting gas, and radiant heat loss rate from flame to surroundings. When coal particle diameter was the same, lean flammability limit was in inverse proportion to the maximum flame propagation velocity obtained by varying the coal concentration. The ratio of maximum flame propagation velocity and lean flammability limit was in proportion to the square of the particle diameter. When the temperature of the volatile flame around particles was uniform, the flame propagation velocities of CO 2/O 2 combustion and N 2/O 2 combustion were the same. The proposed model was provided with inputs of flame propagation velocity for oxy-fuel combustion, and lean flammability limit of air-combustion from fundamental experiments and an industrial-scale burner experiment. By using the model, we simulated variations of flame propagation velocity during operation of oxy-fuel fired plants. In the oxy-fuel combustion technology, correct driving control technology became important.