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High-efficiency, low-emissions (HELE) coal-fired power plant technologies operate with a higher thermal efficiency of the steam cycle for coal-fired power generation, reducing CO₂ emissions per unit energy generation. They represent some of the primary and intermediate solutions to the world’s energy security. Extensive numerical modeling efforts have been undertaken over the past several decades, which have increased our understanding of the technical problems in HELE boilers, including combustion and boiler performance optimization, ash deposition, and material problems at higher operating temperatures and pressures. Overall, the differences in the physical and chemical models, boiler performance, and ash deposition of oxy-fuel combustion in HELE boilers that recirculate CO₂ and H₂O in the boilers are also discussed in comparison with the combustion of coal in the air. This Review comprehensively summarizes the current research on numerical modeling to offer a better understanding of the technical aspects and provides future research requirements of HELE coal-fired boilers, including boiler performance optimization, ash deposition, and material problems. The effects of changes in the configuration and operating conditions are discussed, focusing on the optimization of boiler performance in aspects such as unburnt carbon and NOx emissions. The paper also reviews the retrofit and optimization of operating conditions and the burner geometry with the low-NOx coal combustion technologies necessary to operate the HELE power plants. In terms of ash deposition, the development of submodels, including particle sticking and impacting behaviors and their effects on the deposit growth predictions under different temperatures, are discussed. Numerical models of the material oxidation and creep in the austenitic and nickel-based alloys generally used in HELE conditions have been developed using the finite element method to predict the availability of advanced alloys and creep life in the actual service time of the boiler parts. The predictions of oxide scale growth and exfoliation on the steam-side and fire-side and the creep strength are analyzed. The review also identifies some further research requirements in numerical modeling to achieve the optimization of coal combustion processes and address the technical problems in advanced HELE power plant operations.

This paper discussed the limitation of the laser-induced incandescence (LII) method for the measurement of soot in different laminar pulverized coal flames and explored the soot formation character...

Exploring the transformation mechanisms of sulfur during the superfine comminution plays a crucial role in constructing a coal macromolecular model and developing clean coal technologies. In this w...

In this paper, fine particulate matter (PM) evolution and deposition in pulverized coal combustion are simulated by solving the population balance equation using a quadrature-based method of moment...

Coal gasification fine ash (CGFA) having high carbon content is produced in large quantity as a by-product from coal gasifiers in China. CGFA is usually disposed of by landfill as a solid waste, wh...

In this study, a new technique was developed to measure time-series temperature during the combustion of volatile matter and coal char using magnified two-color pyrometry with high-speed blue backl...

The chemical properties of coal extracts play a crucial role in understanding coal structure, constructing coal model, and developing clean coal technology. However, there is little knowledge about...

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.

Gas-assisted pulverized coal combustion in the laboratory-scale Cambridge Coal Burner configuration CCB1 is studied using a large eddy simulation (LES) coupled with a multistream flamelet/progress ...

Using a developed system that can measure the adhesion force between a spherical fine ash particle and a polished metal surface for superheaters under high-temperature conditions, the adhesion forc...

Currently, volatile matter is generally treated as a postulate substance or a mixture of light gases and tar with given proportion in pulverized coal combustion (PCC) simulation. Whether those trea...

The adverse effect of ultrafine particulate matter (PM) from the combustion of solid fuels calls for fundamental insights to guide effective control strategies. In this work, we investigated the ul...

How to reduce nitrogen oxides in coal combustion process has always been a hot and difficult topic in the research process. In this paper, under the condition of circulating fluidized bed air equivalence ratio of 0.61 and gasification temperature of 970 °C, the partial gasification and combustion method is used to study the influence of the secondary air distribution modes on the gasification and combustion characteristics. Three aspects are discussed in this test: partial gasification characteristics, combustion characteristics, and coal-nitrogen migration and transformation characteristics. The experimental results show that under partial gasification conditions of the circulating fluidized bed, nearly 87% of the fuel nitrogen at the outlet of the circulating fluidized bed is converted into nitrogen in the coal gas, and the ratio of fuel nitrogen to N₂ is about 64.11%, the conversion rate of HCN is about twice that of NH₃, and the combustion reactivity of partial gasification fuels increased at the outlet of circulated fluidized bed. Different secondary air distribution modes will affect the combustion process and the temperature distribution of the combustion chamber. When the secondary air is mixed with the high-temperature coal-based fuel in advance, the entire combustion reaction and the maximum temperature point in the combustion chamber will be moved up. When secondary air is injected simultaneously with high-temperature coal-based fuels, NOₓ emissions are approximately 90 mg/m³ (@6% O₂), the conversion rate of fuel nitrogen to NOₓ is 2.09%, and when nearly half or all of the secondary air is directly premixed into the high-temperature coal-based fuel, the NOₓ emissions are about 70 mg/m³ (@6% O₂), the conversion ratio of fuel nitrogen to NOₓ is reduced to about 1.63%.

The main purpose of this study was to examine the effect of particle size on blending methods for pulverized coals, using a thermo-gravimetric analyzer (TGA) and an entrained drop tube reactor (EDT...

To study ignition and volatile combustion processes of single particles in a group of pulverized coal particles (SPGCPs), the OH signals in the volatile flame were detected by planar laser-induced ...

Petrographic analysis can provide valuable information about pulverized coal used in coal-fired power plants. In this study, petrographic analysis was used to determine the effect of blending on th...

A flat-flame entrained-flow pulverized coal/char reactor (EFR) was designed to study the ignition and combustion characteristics of pyrolyzed bituminous (PB) char particle stream of 53–80 μm size. ...

Morphological analysis of pulverized coal char particles using two-dimensional (2-D) cross-sectional imaging has been widely employed, but its accuracy has not been adequately assessed. In this study, pulverized coal char particles are imaged in three dimensions (3-D) using high-resolution X-ray microcomputed tomography (micro-CT). Particle volume, macropore volume, and macroporosity are measured in three dimensions and analyzed as a function of distance from the particle center using averaging at each radial location. A technique for extracting each particle’s average wall thickness, another morphological parameter used for classification, is also presented based on micro-CT imaging. When applied to pulverized bituminous coal char particles, the micro-CT-based analysis revealed a similar spatial distribution of macroporosity among a population that would typically be classified as containing both group II (mixed porous-solid) and group III (dense) particles. Wall thicknesses determined by micro-CT were g...

A numerical simulation of a pulverized coal jet flame was performed to investigate the physics and flame structure in detail by means of large-eddy simulation with an elementary reaction mechanism....

Soot plays an essential role in radiative heat transfer in pulverized coal boilers, but the controlling processes that cause different soot behaviors in O2/N2 and O2/CO2 atmospheres are not clear. ...

This paper presents a synthesis of a large body of experimental data on growth rates of ash deposits from the air and oxy-combustion of multiple pulverized solid fuels, including coal, biomass, and their blends. The experimental data were obtained from 35 tests in a 100 kW (rated) entrained-flow combustor that allowed for self-sustained combustion of solid fuels. Ash deposition rates were measured using a wall-temperature-controlled ash deposition probe. The collected deposits were divided into tightly bound “inside deposits” adjacent to the heat transfer surface and loosely bound “outside deposits” that grow further out. Ash aerosol particle size distributions (psd’s) and size-segregated compositions were obtained through electric mobility, light scattering, and impactor methods. Rates of ash deposition for both inside and outside deposits are presented. Rates of growth of the inside deposit were proportional to the sub-micrometer particle (PM1) concentration in the flue gas but correlated poorly with th...

The entrained flow reactor (EFR) is frequently applied to analyze the reactivity of pulverized coal char under controlled atmospheres of temperature and partial pressure. The rate constants for a s...

In this paper, the characteristics of NOx reduction by reagent injection into the fuel-rich zone (RIFR) in coal combustion were investigated, under high temperatures and reducing atmosphere conditions. The stoichiometry and temperature have a major influence on the chemistry of NO and NH3 reagent (ammonia or urea). Therefore, experiments were conducted on a bench-scale test system with urea solution as the reagent to investigate the key factors influencing NOx reduction, including primary stoichiometric ratio (SR1), temperature in the reaction zone, and normalized stoichiometric ratio (NSR) of the injected reagent. The results indicated that the primary stoichiometric ratio SR1 was the key parameter affecting the reduction of NOx emissions. Better NOx reduction was achieved with a decrease in the SR1 for bare air staging. However, there was no benefit for NOx reduction by reagent injection in the very fuel-rich zone (SR1 ≤ 0.75), which depended on the distribution of N-intermediates and initial NO concent...

A novel system consisting of an online ash-deposition thermogravimetric analyzer coupled with an electrically heated down-fired furnace was developed for pulverized coal combustion. A steady high-t...

In pulverized coal combustion plants, low-grade sub-bituminous coal is known to cause adhesion of fly ash and its growth on the surface of the super heater, heat exchanger, and furnace walls, even when cocombusted with high-grade bituminous coal. In this study, six different fly ash samples collected from commercial pulverized coal combustion plants were investigated to find if the porosity and the liquid phase would have a significant impact on the tensile strength of the ash powder beds. Herein, we demonstrate that the use of alumina (Al2O3) nanoparticles as an additive is highly effective in preventing such troublesome events, which would be a great aid to facilitate stable and long-term operation of coal combustion plants. The function of Al2O3 nanoparticles is found to be 2-fold: retaining the porosity and perturbing the chemical composition of the ash samples. This is rationally supported by experimental and theoretical results. The key to our study is a split-type tensile strength tester that can d...

Eccentric-swirl-secondary-air combustion technology (ESSACT) has been applied to a 300 MWe anthracite- and down-fired boiler with swirl burners. To improve burnout performance of the retrofitted boiler, the effects of primary air ratios on flow and combustion characteristics are investigated via cold-model aerodynamic experiments and industrial experiments. When primary air ratios are 17.09 and 19.08%, a deflective flow field occurs, and with increasing the primary air ratio from 21.11 to 24.75%, a symmetrical “W” flow field is formed. With increasing the primary air ratio from 17.09 to 24.75%, the maximum dimensionless vertical velocity of air flow near the front wall increases linearly from 0.364 to 0.521. Accordingly, the penetration depth in the real boiler increases by approximately 2.88 m. For a primary air ratio of 18.47%, the temperatures at the burner exit and in the furnace hopper near the front and rear walls are both seriously asymmetrical and the combustion path of pulverized coal particles b...

This study presents the Raman spectroscopy analysis of the carbon structure on the surface of pulverized coal char particles sampled at different positions in a pilot-scale blowpipe. To evaluate the degree of char oxidation, we compared the experimental data of the samples before and after mild oxidation. The results showed that the surface crystallinity of large char particles before mild oxidation increased, irrespective of the sampling position in the radial direction. This suggested that large particles were exposed to higher temperatures than small particles in the blowpipe. Moreover, the surface crystallinity of the small char particles before and after mild oxidation was almost the same. This indicated that the small particles had already been oxidized in the blowpipe. On the other hand, the surface crystallinity of the large char particles changed drastically after mild oxidation. This was because large particles passed through an oxygen-lean region and the char oxidation of these particles did no...

This paper reports the oxy-fuel combustion characteristics in a pilot-scale furnace with a bituminous coal. After discussing the design principles of oxy-fuel burners in detail, a swirling low-NOx ...

This work reports a newly preheated system with pulverized coal oxy-fuel moderate or intense low-oxygen dilution (MILD) combustion for low NOx emissions. During the experiment, high-temperature fue...

The direct combustion of recyclable metals has the potential to become a zero-carbon energy production alternative, much needed to alleviate the effects of global climate change caused by the increased emissions of the greenhouse gas CO2. In this work, we show that the emission of CO2 is insignificant during the combustion of pulverized sponge iron compared to that of pulverized coal combustion. The emissions of the other harmful pollutants NOx and SO2 were 25 and over 30 times lower, respectively, than in the case of pulverized coal combustion. Furthermore, 96 wt % of the solid combustion products consisted of micrometer-sized, solid or hollow hematite (α-Fe2O3) spheres. The remaining 4 wt % of products was maghemite (γ-Fe2O3) nanoparticles. According to thermodynamic calculations, this product composition implies near-complete combustion, with a conversion above 98%. The results presented in this work strongly suggest that sponge iron is a clean energy carrier and may become a substitute to pulverized c...

The present work investigated the correlations of the particulate matter with an aerodynamic diameter of

This study reports an experimental investigation on the nitrogen oxide (NOx) emissions in pulverized fuel (coal and char) combustion through preheating with a circulating fluidized bed. The high-te...

As a novel combustion technology, flameless combustion is attractive to achieve highly efficient and low NOX utilization of fuels. In this paper, a new method to realize flameless combustion of pulverized coal based on coal preheating technology was adopted. Experimental research on flameless combustion was implemented with pulverized coal in a 30 kW coal preheating and combustion test rig. In the study, coal preheated characteristics, combustion behavior, and the formation mechanism of NOX are discussed. The results show that the temperature of pulverized coal can be preheated up to above 850 °C, and most of the volatiles are released during the preheating process. Only 33.90% of the fixed carbon in pulverized coal is converted into coal gas and most remains in the high temperature coal char, and 91.14% of the fuel-N released from pulverized coal is converted to N2. Stable flameless combustion can be achieved with preheated fuels in the down-fired combustor, and no obvious flame front can be observed thr...

Air-staged combustion is one of the most sophisticated and effective technologies for reducing NOx emission during pulverized coal combustion. However, it may also result in problems of high-temperature corrosion, slagging, and high-imperfect/incomplete combustion loss. In order to prevent these problems, the multihole wall air coupling with air-staged technology (MH&AS) has been developed. The aim of this work is to investigate the impact of MH&AS on NOx emission by applying a laboratory scale of a MH&AS furnace. The results show that there existed an optimal multihole wall air ratio to significantly reduce the NOx emission. For example, with burner air ratios of 0.6, 0.7, 0.8, and 0.9, the corresponding optimal multihole wall air ratios were 0.100, 0.075, 0.050 and 0.025, respectively. The air distribution mode with a smaller burner air ratio and its optimal multihole wall air ratio were more conducive for NOx reduction. Furthermore, the influence of coal properties on NOx emission was also evaluated. T...

Low-NOx combustion technologies are widely applied in pulverized coal-fired boilers. But it promotes the formation of high concentration of H2S, which is one of the main reasons for high-temperature corrosion. To limit the H2S formation, it is urgently necessary to reveal the evolution behavior of the sulfur species. In this work, the reaction mechanism for sulfur species was investigated using a tube-heating furnace for low-sulfur bituminous coal combustion. In the primary stage of combustion, the O2 concentration decreased sharply. Meanwhile, the sulfur species of SO2, H2S, COS and CS2, and significant amount of reductive gases CO and H2, were generated. After the sulfur release finished, the distribution of the sulfur species in the downstream region depended on only the gas-phase reactions. With the reduction of CO and H2, part of SO2 was converted to H2S and COS. There also exited some shift relationships among SO2, H2S, COS, and CS2 in the presence of abundant of CO2 and H2O. On the basis of the exp...

The present work aims to model ash vaporization from a burning char particle during pulverized coal combustion in an oxygen-enriched O2/CO2 atmosphere. The modeling development was to apply the classic ash vaporization model of Quann and Sarofim to cover oxy-coal combustion over a wide range of O2 concentrations by coupling it with the double-film char burning submodel to properly describe the burning process of a single char particle. The model was extensively validated with literature data on the vaporization of SiO2, MgO, and CaO in both O2/N2 and O2/CO2 atmospheres. The model was proved to be able to predict the vaporization behavior of SiO2 during char conversion stages in both atmospheres, covering the effects of coal type, particle size, and O2 concentration. The model predicts the vaporization of MgO and CaO during char combustion of bituminous coal, but improvement is required to describe the vaporization of MgO and CaO during char combustion of lower-rank coals by considering the occurrence of M...

Zhundong coal (ZDc) with a large reserve is faced with severe slagging and fouling during combustion in pulverized coal furnaces because of its high Na content. Due to the low-temperature reaction characteristics of a circulating fluidized bed (CFB), the ash-related problems might be alleviated when ZDc is used as fuel in a CFB. In this study, the slagging and fouling characteristics of three types of ZDc were tested in a 0.4 t/d CFB test system. The influences of three aspects including reaction temperature, reaction atmosphere, and coal property were studied in order to realize the utilization of ZDc in the CFB. Experimental results indicate that slagging and fouling still occurred in the CFB. During gasification, ZDc displayed slagging behaviors in the riser, which was closely related to the used bed material of quartz sand. The slagging degree was increased with the rise of reaction temperature. In different reaction atmospheres, the migration and transformation behaviors of Na differed, which further...

Biomass is a carbon-neutral fuel and has a potential to be used in pulverized coal injection (PCI) technology in ironmaking blast furnaces (BFs). Compared with pulverized coal particles, biomass particles vary considerably in particle shape, and thus the change of aspect ratio of biomass particles may affect the motion and conversion of biomass particles. In this study, a computational fluid dynamics (CFD) model is developed to simulate the flow and thermo-chemical behaviors related to biomass injection into BFs. The model features non-spherical particle shapes and an improved devolatilization model. The model is then applied to a pilot-scale test of charcoal injection using a pilot-scale PCI test rig under simulated BF conditions for model validation. The burnout comparisons between simulation and measurement indicate that compared to spherical particles, the non-spherical particles show smaller burnouts due to the shorter travelling time in the chamber; moreover, the burnouts predicted by the model cons...

To further advance pulverized coal (PC) combustion theory and enable the rational development of horizontal bias combustion technology, combustion experiments were conducted in a 250 kW pilot-scale bias combustion simulator; multiple research means of combustion temperatures, flame spectra, burnout rates of residual solids, and NOx formation were used. A blend of sub-bituminous coal from Indonesia and bituminous coal from Australia was tested. The effects of bias concentration ratio (BCR) on the ignition characteristics of parallel bias PC jets in a reducing atmosphere were investigated. The results indicate that with increasing BCR for parallel bias PC jets, the standoff distance gradually decreased; the peaks of subsequent combustion temperature and visible-light intensity gradually increased; the continuous flame regions became advanced and concentrated; the flame stability gradually increased; the burnout rate gradually increased; the NOx formation gradually decreased, and the ignition characteristics...

Carbonaceous aerosols, including organic carbon aerosols and black carbon aerosols, are produced by the combustion of pulverized coal even under fuel-lean conditions. These carbonaceous aerosols can be particularly hazardous to human health. In this study, the chemical compositions and formation pathways of organic aerosols emitted during the combustion of high-sulfur-content coals were investigated. It was found that nitrogen-containing organic matter contains a significant proportion of organic aerosol mass from the combustion of high-sulfur-content coals, which is not the case for organic aerosols generated during the combustion of low-sulfur-content coals. The formation of organic aerosols was significantly enhanced when higher-sulfur-content coal was burned. A strong correlation between organic aerosol mass and the sulfate concentration was observed. It is proposed that acidic sulfate particles absorb the nitrogen-containing organic volatiles produced by coal pyrolysis onto the particle phase through...

Effects of external and internal catalysts on anthracite combustion reactivity and kinetics were investigated using the method of differential thermal analysis (DTA). It was found that the combustion reactivity of both raw and demineralized anthracites was all apparently improved by the introduction of CeO2 and Fe2O3. When CeO2 and Fe2O3 were used in raw anthracite, the combustion starting time from the DTA curve was advanced from 1470 to 1312 and 1325 s, respectively, as compared to the improvements from 1285 to 1089 and 1055 s while adding the same amounts of CeO2 and Fe2O3 into demineralized anthracite. The addition of catalysts has increased the combustion rate for raw anthracite much more significantly than that for demineralized anthracite. Reformed differential thermal analysis (RDTA, change the reference material from Al2O3 to raw anthracite) showed a direct effect of catalysts on its combustion, which broadly agreed with the results of the DTA study. The inherent mineral matter at high contents c...

To reduce the amount of CO2 emissions from exhaust gas with a high temperature inside a flue of a converter, one new process, performed by injecting pulverized coal (PC) into the hotter gas using its waste heat gas to generate CO, is proposed. Numerical, experimental, and industrial investigations are conducted. The effects of the temperature, gas component, and coal size on the conversed effect of CO2 and O2 were analyzed in the experiments, and the transient products were described during the PC injection using a high-temperature drop-tube furnace. The effects of the injecting angle and gun number on the mixed distribution of PC in flue gas were discussed by simulated analyses. The results show that the specific surface area of PC was 28.5620 m2 g–1, whereas the specific surface area of coke char (CC) was 13.6815 m2 g–1 using the Brunauer–Emmett–Teller method. The porosity volume V value of PC was 0.0113 mL g–1 with an average porosity size of 0.8185 nm. The V value of CC was 0.0056 mL g–1 with an avera...

To further understand the bias combustion behavior of new coal used for horizontal bias combustion and obtain its characteristic parameters, combustion experiments were conducted in a 250-kW pilot-scale bias combustion simulator; multiple research measurements of flame spectra, combustion temperatures, and burnout rates of residual solids were used. Bituminous coal from Australia, sub-bituminous coal from Indonesia, and a blend of these coals were tested. The effects of the raw-coal equivalent moisture (RCEM), pulverized-coal fineness (PCF), and coal type on the ignition characteristics of parallel-bias pulverized-coal jets in a reducing atmosphere were investigated. The results indicate that, with decreasing RCEM and PCF, the standoff distance gradually decreased, the flame stability gradually increased, the burnout rate gradually increased, and the ignition characteristics gradually improved. The RCEM had negative effects on ignition in the early stage but positive effects during subsequent combustion. ...

The present work evaluates the feasibility to capture at least 85% of the CO2 emitted by an advanced supercritical pulverized coal power plant of 800 MWe, delivering a CO2 product with a purity of 95% (dry basis) or higher, using an adsorption-based postcombustion capture process based on carbon honeycomb monoliths regenerated by steam stripping. Process performance has been evaluated through the dynamic simulation of the cyclic adsorption process. The fixed bed adsorption model, which was validated against experimental results, is based on the mass, momentum, and energy conservation equations, and it accounts for competitive adsorption between the three main flue gas components: N2, CO2, and H2O. The evaluated TSA process meets the targets for the capture rate and product purity, with a heat duty of 3.59 MJ kg–1 CO2, which is close to the specific reboiler duty of the benchmark amine-based absorption process. Materials and process development will lead to lower duties. A sensitivity analysis was carried out, and it has shown that slightly faster adsorption kinetics for CO2 could drop the specific heat duty of the process to 2.89 MJ kg–1 CO2, which is lower than that of the benchmark technology. From the process point of view, the use of waste heat from the power plant could further reduce the energy penalty of the integrated CO2 capture process., Work carried out with financial support from the HiPerCap Project of the European Union 7th Framework Programme (FP7) (2007−2013; Grant Agreement No. 608555), We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

The near-wall air (NWA) technology is effective for resolving the high-temperature corrosion on water tube walls in large-scale utility boilers. A numerical investigation was performed to study the effect of NWA on combustion and high-temperature corrosion in an opposed firing pulverized-coal 300 MWe utility boiler. The consistency between the in situ measured and simulated CO distribution tendencies proved that the current simulation methods were reliable and appropriate. NWA not only reduced the peaks of the CO and H2S concentrations but also significantly decreased the zone with high CO and H2S near the side walls. The NWA injection weakened the reducing atmosphere on the side wall by 40%. NWA presented a slight impact on the gas temperature and the nitrogen oxide (NOx) concentration at the furnace outlet and led to an obvious increase in unburned carbon. The flow ratio of the NWA was analyzed from 3% to 12%. Considering the unburned carbon, CO, and H2S distribution, the appropriate NWA ratio was appro...

Pressurized pneumatic conveying plays an important role in large-scale coal gasification systems. Some of the underlying mechanisms affecting the conveying characteristics remain open issues. Phase diagrams can provide key information regarding flow characteristics by revealing the relationship between pressure drop and superficial gas velocity, which can be utilized for flow pattern identification, stability analysis, and system optimization, in an economic and feasible way. The present work experimentally investigated phase diagrams of pressurized pneumatic conveying on a pilot-scale setup, with three types of the most widely used pulverized coal in China selected as the conveyed materials. The effects of superficial gas velocity, solid-phase mass flow rate, pipeline layout, particle size, coal type, and moisture content were studied, respectively. The findings will contribute to a better understanding of the underlying mechanism of pressurized pneumatic conveying with pulverized coal, and to a better g...

Studies on coal pyrolysis via a thermogravimetric analyzer (TGA) are typically performed under a variety of temperature increases beginning at ambient temperature. A main limitation in these procedures is that the reaction temperatures (generally lower than 1000 °C) are typically lower than those met in pulverized coal boilers and ash flow temperatures (AFTs; generally higher than 1100 °C). In this paper, five Chinese coals are clarified to low- or mid-AFT coals as their AFTs increase. They were then prepared in TGA at several temperatures below or above their AFTs under N2 atmosphere for approximately 30 min after a heating procedure at a rate of 80 °C/min. The coal and residual char samples were collected and analyzed via X-ray diffraction and compared to the chemical thermodynamic calculation. The secondary weight loss appeared between 1200 and 1450 °C in the TG curves of four mid-AFT coals but not the low-AFT coal. The results showed that this secondary weight loss was caused by the carbothermal reduc...

The stabilization mechanism of a turbulent lifted pulverized coal jet flame in a heated coflow is investigated by means of three-dimensional direct numerical simulation. The coal particles are tracked in the Lagrangian frame with experience of moisture evaporation, volatile releasing, and carbon combustion. The devolatilization process is modeled with a competing two-step model, and the carbon reaction is described by a single-film model. It is found that the mean velocities for the gas-phase and particles can develop into self-similar profiles, while the fluctuation velocities have not achieved the self-similar status. The turbulence can be enhanced by ignition and combustion processes. By investigating the correlations among the temperatures, heat release rate, and devolatilization rate, it is found that autoignition of the volatile is the key mechanism responsible for coal flame stabilization under the present condition. The heating effects from the stripe flames in the shear layers, heated coflow, and...