Coal Oxy-fuel Combustion Research Articles

CFD Analysis on the Effect of Ammonia Addition on Oxyfuel Coal Combustion in a Swirl Burner

CFD Analysis on the Effect of Ammonia Addition on Oxyfuel Coal Combustion in a Swirl Burner

Effects of SO2 and H2O on the ash deposition and NO emission during oxy-fuel combustion of high-alkali coal

The oxy-fuel combustion is promising to realize the large-scale CO2 capture and effective reduction of nitric oxides. The recirculation of flue gas in oxy-fuel combustion can lead to high concentrations of SO2 and H2O, which probably affects the ash deposition of high-alkali coal because SO2 and H2O are important for the transformation of alkali and alkaline earth metals (AAEMs). In the present work, the effects of SO2 and H2O in recycled flue gas on the ash deposition and NO emission during the oxy-fuel combustion of high-alkali coal were experimentally evaluated in a vertical two-stage furnace system. The conversion ratio of fuel-nitrogen to NO (CNO) and ash deposition efficiency were measured, and then the ash deposits were subjected to a couple of tests for further analyses. The experimental results show that SO2 helps to reduce the NO emission and its impact on ash deposition depends heavily on its concentration. In the case with modest SO2 addition, the sulfations of sodium and calcium are enhanced to some extent. Consequently, the amount of small sticky particles (NaCl and sodium aluminosilicates) that attached to large particles decreases, and the large particles mainly made of calcium aluminosilicates become smaller and less sticky. The newly generated Na2SO4 and CaSO4 are insufficient to overcome the inhibiting effects, thus the ash deposition efficiency decreases. Under the condition of excessive SO2 addition, the sulfations are further promoted. The small particles rich in Na2SO4 and CaSO4 are substantially more, which can not only serve as the initial ash layer on the heating surface, but also strengthen the stickiness of large particles by attaching to their surfaces. Therefore, the ash deposition efficiency increases·H2O can reduce the NO emission, while it aggravates the ash deposition because H2O enhances the sulfation.

Oxy-fuel combustion of pulverized coal in an industrial boiler with a tangentially fired furnace

Numerical studies of the processes of oxy-fuel combustion of pulverized coal (PC) in an industrial boiler BKZ 500–140–1 (with a capacity of about 400 MW) were carried out in this work. The proposed comprehensive mathematical model was tested based on data from a full-scale experiment (2.4 MW laboratory stand) of oxy-fuel combustion of PC. The conducted comparison has shown a good agreement of the calculation results with the experimental data. A detailed comparative analysis of the effect of the operating modes of the BKZ 500–140–1 industrial boiler during oxy-fuel combustion of coal on physical and chemical processes and the level of harmful emissions (NOx, CO2) was performed for the first time. The effect of oxygen concentration and CO2/H2O ratio in the blast on the processes of ignition and combustion of fuel in a nitrogen-free environment has been studied. It is shown that when nitrogen in the blast composition is replaced with flue gases without changing the oxygen concentration in the boiler under study, the average temperature in the furnace volume declines, as well as the average heat flux at the walls decreases from 87.35 to 70.32 kW/m2. To achieve the standard operating parameters of the BKZ 500–140–1 industrial boiler, it is necessary to increase the oxygen concentration in the blast from 15.4 to 19.7 vol.% (i.e. by 28%). The implementation of the oxy-fuel combustion technology on a steam boiler leads to a decrease in the NOx concentration in flue gases from 480 to 273 mg/m3.

Experimental study on NO emission and ash deposition during oxy-fuel combustion of high-alkali coal under oxygen-staged conditions

The oxygen-staged combustion is an effective strategy to reduce NO emission, but its effects on ash deposition in oxy-fuel combustion of Zhundong high-alkali coal still remain unclear. This paper simultaneously focused on the NO emission and ash deposition during the oxygen-staged oxy-fuel combustion of Zhundong coal using a vertical two-stage furnace system. The air- and oxygen-staged combustion were compared and the impacts of oxygen content and stoichiometric ratio in primary zone (SR1) in oxygen-staged combustion were further evaluated. The results show that compared to air-staged combustion, the oxygen-staged case in oxy-fuel combustion leads to smaller conversion ratio of fuel-N to NO (XNO) and smaller mass of ash deposit. Under oxygen-staged conditions, both the XNO and deposit mass have an upward trend as the oxygen content increases (15%–50%). About 20 mg more ash could be collected for every 10% increase in oxygen content. The XNO increases when SR1 gets elevated from 0.5 to 1.2, however, the deposit mass exhibits a downtrend at SR1 ≤ 0.9 and becomes nearly independent of oxygen supply when the SR1 further increases. The SR1 of 0.9 is a reasonable choice, and some measures should be taken to alleviate the ash-related problems if smaller SR1 is needed.

Flamelet LES of swirl-stabilized oxy-fuel flames using directly coupled multi-step solid fuel kinetics

In this work, a new Large-Eddy Simulation (LES) based approach coupled to a flamelet description of the gas-phase and seamless detailed solid-fuel kinetics is introduced and applied to a self-sustained oxy-fuel coal combustion chamber. LES enables a detailed description of the turbulent flow field, mixing, and heat transfer. The latter also includes thermal radiation for the particles and solving the radiative transport equation using the weighted sum of gray gases for the gas phase. The flamelet description of the gas phase represents an accurate and computationally efficient way to include turbulence-chemistry interactions taking into account the reaction of the complex gas mixture released from the solid fuel particles. For the first time, these two detailed models are coupled with a recently developed solid-fuel kinetic mechanism, allowing of the entire particle conversion process, i.e., devolatilization and char oxidation, to be seamlessly included in the simulation. After the required coupling strategies are discussed, the holistic model is applied to an oxy-fuel combustion chamber. Firstly, the results are extensively validated by the available measurements. Secondly, comparisons to state-of-the-art simplified solid fuel kinetics are carried out to assess the interaction of detailed solid-fuel kinetics with the other models.

Pollutant Emissions during Oxy-Fuel Combustion of Biomass in a Bench Scale CFB Combustor

Nowadays oxy-fuel combustion of coal and biomass is the most promising option for the reduction of CO2 emissions from power plants. In this paper, emissions of NOx (NO, NO2, N2O and their precursors, such as NH3 and HCN), SO2 and CO during conventional and oxy-fuel combustion of three kinds of biomass (agro, woody and energy crop) and a reference coal are presented and discussed. Combustion tests were conducted at 850 °C in the laboratory-scale circulating fluidized bed (CFB) reactor in air and O2/CO2 atmospheres. A FTIR spectrometer was used to measure instantaneous concentrations of all pollutants in the flue gas. Emissions of SO2, N2O and CO for the combustion of biomass in all atmospheres were lower than those for the combustion of reference coal. It was found that oxidation of nitrogen species released with volatile matter was responsible for high emissions of NOx during combustion of biomass fuels in air and mixtures of O2 and CO2. The lowest NO emissions for tested fuels were detected in oxy-21 atmosphere (21% O2/70% CO2). Oxy-combustion of biomass in O2/CO2 mixtures at 30% and 40% O2 caused a decrease in emissions of N2O and CO while NO and SO2 emissions increased. The results of this study show that the tested biomass fuels are ideal renewable energy resources both in conventional and oxy-fuel conditions with a minor potential for environmental pollution.

A Comprehensive Review of Ash Issues in Oxyfuel Combustion of Coal and Biomass: Mineral Matter Transformation, Ash Formation, and Deposition

To alleviate the global warming issue, various CO2 abatement technologies have been proposed. As one of the leading options for CO2 capture in power plants mostly firing coal and biomass, the oxyfuel combustion technology has been actively developed for decades. Progress at different stages of the development has been continuously updated in several reviews. However, they usually cover a wide range of topics, which vary significantly in detail. The ash issues are very critical to the design and operation of oxyfuel boilers, but may be one of the most controversial topics. The knowledge is widely scattered in different research articles, and a relatively comprehensive description is not available in the published reviews. Therefore, it is difficult for one to have a clearer picture of this important topic. The present review attempts to provide a more complete understanding. It pays particular attention to experimental data, because they are the basis for model development and full-scale simulation. Different from previous reviews that presented limited information on mineral matter transformation under oxyfuel conditions, this Review summarizes most of the related results reported in the open literature. Data on ash formation and deposition in oxyfuel combustion are also updated. They are organized according to different combustion technologies, i.e., oxyfuel pulverized fuel combustion (oxy-PFC) and oxyfuel fluidized bed combustion (oxy-FBC). By correlating between the three aspects, an in-depth understanding of ash issues in oxyfuel combustion may be achieved. At the end of this Review, key messages regarding mineral matter transformation, ash formation and deposition in oxyfuel combustion, and future research needs are presented.

Oxy-Fuel Combustion of Hard Coal, Wheat Straw, and Solid Recovered Fuel in a 200 kWth Calcium Looping CFB Calciner

The fluidized bed combustion (FBC) of biomass and solid recovered fuel (SRF) is globally emerging as a viable solution to achieve net-negative carbon emissions in the heat and power sector. Contrary to conventional fossil fuels, alternative fuels are highly heterogeneous, and usually contain increased amounts of alkaline metals and chlorine. Hence, experimental studies are mandatory in order to thoroughly characterize the combustion behavior and pollutant formation of non-conventional fuels in novel applications. This work gives an overview of experimental investigations on the oxy-fuel combustion of hard coal, wheat straw, and SRF with a limestone bed in a semi-industrial circulating fluidized bed (CFB) pilot plant. The CFB combustor was able to be operated under different fuel blending ratios and inlet O2 concentrations, showing a stable hydrodynamic behavior over many hours of continuous operation. The boundary conditions introduced in this study are expected to prevail in carbon capture and storage (CCS) processes, such as the oxy-fuel combustion in the CFB calciner of a Calcium Looping (CaL) cycle for post-combustion CO2 capture.

NOx Reduction Using Pilot-Scale SCR Under Oxyfuel Conditions

This paper presents a comprehensive experimental study of selective catalytic reduction (SCR) of nitrogen oxides formed in the oxyfuel combustion of lignite coal in a 500 kWth pilot-scale bubbling fluidized bed (BFB) boiler using the V2O5 over TiO2 honeycomb catalyst and the ammonia as the reducing agent. The study also compares the performance of the SCR between oxyfuel and air combustion modes. The SCR unit is placed in the tail-end position of the flue gas processing scheme after the cyclone particle separator. Experiments were realized both in air- and oxyfuel combustion regime, evaluating the impact of relevant process conditions on the NOx reduction. The dependence of the NOx reduction efficiency on the catalyst temperature and on the normalized stoichiometric ratio (NSR) of the reducing agent molar flow to the molar flow of NOx were studied. The efficiency of the NOx reduction was evaluated based on the NOx concentration measured simultaneously before and after the SCR unit. In the off-gas, the concentration of unreacted reducing agent (ammonia slip) was measured as well. For evaluation of real NSR, ammonia and flue gas flow rates were measured during each experiment. The catalyst temperature was regulated within the experiments in the range of 260 to 300 °C and the NSR was chosen in the range of 0 to 1.2. From this experimental setup, the correlations of the NOx reduction efficiency related to the different NSR and catalyst temperature were evaluated. The results show the fundamental information about the differences between air and oxyfuel conditions in a real combustion environment. In general, the NOx conversion efficiency was significantly higher during air combustion. In order to get similar results of maximum NOx conversion as reached during air combustion, it was necessary to increase NSR up to 1.8 and more, however at the cost of significantly increased ammonia slip. Although the SCR performance is lower in oxyfuel combustion, it was possible to decrease NOX under 100 ppmv with NSR about 1 and without any significant ammonia slip, which is important prior to further CO2 treatment.

Thermodynamic analysis of oxy-fuel combustion integrated with the sCO2 Brayton cycle for combined heat and power production

The supercritical CO2 (sCO2) Brayton cycle is highly efficient in terms of its power production efficiency and is also compact in structure. It is therefore expected to substitute the steam Rankine cycle in various applications. In addition, the high temperature heat that is disposed to the heat sink in the sCO2 cycle can be further utilized to increase the economy and profitability of the plant. In this paper, we report the integration of the sCO2 cycle with single-stage reheating and recompression with the pulverized coal oxy-fuel combustion process for combined heat and power production. The integrated system was analyzed in terms of its thermodynamic performance, including its electrical efficiency and heating efficiency. For oxy-fuel combustion, different flue gas recycling modes, i.e., wet mode and dry mode, were compared. Under the basic sCO2 cycle conditions of 30 MPa/600 °C/600 °C, the electrical efficiencies for the wet and dry modes were 36.6 and 35.3%, respectively, while the corresponding heating efficiencies were 15.4 and 14.9%, respectively, with a total efficiency of 52.0% for the wet mode and 50.2% for the dry mode. Furthermore, the CO2 capture rate was determined to be ~99.94%. Sensitivity analysis was conducted, and the influences of the turbine inlet temperature, turbine inlet pressure, oxygen concentration, turbine outlet pressure, and split ratio in the high-temperature recuperator were investigated. Finally, the residual heat from the air separation unit and the flue gas was recovered and integrated with the sCO2 cycle, and it was found that the heat recovery decreased the split ratio to recompression and could add a 0.3–2.7 percentage point increment to the electrical efficiency, in addition to a 0.3–2.1 percentage point increment to the heating efficiency.

Reaction behaviors of a single coal char particle affected by oxygen and steam under oxy-fuel combustion

The reaction behaviors of coal char particles tend to become more complex with the presence of gasification reaction under mixtures of O2/CO2/H2O, which is an urgent demand for the better understandings of pulverized coal oxy-fuel combustion with wet recycle. In this paper, numerical simulations are adopted to evaluate the individual effects of O2 and steam concentration on the reaction behaviors of a single coal char particle. The results reveal that, as the steam content increases from 0% to 10%, both the peak and surface temperatures increase by 600 K and 30 K, respectively. As the steam level continues to increase, the peak temperature increases slightly and the surface temperature is hardly changed. The formation of H2 can be promoted by the addition of steam, while that of CO is attributed to the increased O2 level. The sensibility of O2 and steam content on the homogeneous reactions follows R1 (CO + 0.5O2 + H2O → CO2 + H2O) > R3 (CO2 + H2 → CO + H2O) > R2 (CO + H2O → CO2 + H2), and the H2O molecules in R1 play the roles of both reactant and catalyst. The reaction of char-CO2 affected by the char-H2O is dependent on steam level. Strengthening the char reaction with H2O can benefit the char reaction with CO2 at below 20% steam level, while adverse to the char-CO2 reaction at above 20% steam level. The increase in O2 content promotes the char-CO2 reaction but slightly inhibits the char reaction with H2O. Furthermore, the carbon consumption rate can be improved by the increase in O2 level because both oxidation and gasification reactions are enhanced. As the steam concentration increases, the carbon consumption rate evidently decreases at first, but slightly increases thereafter because of the enhanced char-H2O reaction.

Pressurized oxy-fuel combustion of a char particle in the fluidized bed combustor

Pressurized oxy-fuel combustion of coal in fluidized bed (FB) holds the potential to realize low-cost CO2 capture. However, the fundamental study in this manner is still rare due to the difficult access to the pressurized oxy-FB combustion tests. In this work, the experimental study of single char combustion was firstly conducted in a visualized pressurized FB combustor under various operating conditions. Then an experimentally verified particle-scale char combustion model was developed to reveal the dependence of char combustion on parameters. Results showed that the char conversion was accelerated with the increase of pressure, mainly due to the high oxygen diffusion and char gasification. The gasification played a non-negligible role in pressurized oxy-fuel combustion, especially under high oxygen concentration and bed temperature. Increasing oxygen concentration and bed temperature not only promotes the char oxidation rate and particle temperature, but also increases the gasification rate and the share of char conversion via gasification, resulting in shortening the burnout time of char. In addition, a higher fluidization number lowered both the burnout time and peak temperature of char particle, due to the simultaneous improvement of mass and heat transfer. The influences of char size and fluidization number on char gasification conversion ratio are very weak. In addition, the quantitative analysis of the influence of different operating parameters on the combustion process was obtained by model sensitivity analysis.

Three-dimensional simulation of the co-firing of coal and biomass in an oxy-fuel fluidized bed

The co-firing of coal and biomass in fluidized beds under oxy-fuel conditions is an important approach with significant industrial prospects, for both carbon dioxide capture and disposal of biomass waste produced by agriculture and forestry. Numerical simulation is essential in the design of structural and operational parameters for oxy-fuel fluidized beds, as is experimentation. Following our previous research on the oxy-fuel combustion of coal in a fluidized bed (Powder Technol. 2019, 349, 40–51), this paper develops 3D Eulerian-Lagrangian simulations for the co-firing of coal and biomass in an oxy-fuel fluidized bed based on the multiphase particle-in-cell (MP-PIC) scheme. The particle field is described by the discrete particle method (DPM) and the gas field is calculated by large eddy simulation (LES). Different models are used for the reaction of coal and biomass, including devolatilization, combustion of char and volatiles, and the production of pollutants. The numerical simulation was verified by combustion experiments carried out in a micro-fluidized bed reactor with an online mass spectrometer. Based on the simulations, the effects of biomass mass ratio, combustion atmosphere, oxygen concentration, and combustion temperature on the co-firing of coal and biomass in an oxy-fuel fluidized bed are discussed.

3D simulation on pressurized oxy-fuel combustion of coal in fluidized bed

Pressurized oxy-fuel combustion technology is considered as a perspective carbon capture technology in industrial process. A computational fluid dynamics (CFD) model based on Multi-Phase Particle-In-Cell (MP–PIC) method was developed to predict pressurized oxy-coal combustion process in fluidized bed. The heterogeneous and homogeneous combustion reactions of coal were considered in this model. The predicted results were validated the accuracy of this model with experimental data from a 15 kWth pressurized fluidized bed combustor in terms of the gas component and temperature characteristics. The characteristics of gas–solid flow and combustion under different pressure (0.1–2 MPa) and oxygen atmosphere were studied in this work. The predicted results show that the intensity of particle motion and the expansion degree in the fluidized bed was gradually decreased with an increase in pressure. A correlation was proposed based on the simulation results to maintain suitable fluidization conditions in pressurized circulating fluidized bed at different pressures. The temperature of particle phase region gradually increased with combustion pressure and inlet O2 concentration increased. In addition, the CO2 concentration in outlet increased while the emission of CO and NOx decreased as the combustion pressure increased.

CO2-mediated sulfur evolution chemistry of pyrite oxidation during oxy-fuel combustion

Ash slagging caused by pyrite (FeS2) transformation in coal-fired boilers is accompanied by sulfur evolution from pyrite oxidation during oxy-fuel coal combustion. Theoretical studies based on density functional theory (DFT) were performed to systematically understand the temperature-dependent sulfur evolution chemistry of CO2-assisted pyrite oxidation. The results show that there is a strong interaction between CO2 and FeS2 surface. The interaction intensity is promoted by the presence of surface O atom. The adsorbed CO2 molecule dissociates into CO molecule and active surface O atom, which can supply oxygen source for SO2 formation. CO molecule strips a lattice sulfur atom from FeS2 surface to generate COS species. CO2 decomposition on FeS2 surface at 1073 K is activated by 677.73 kJ/mol, and exothermic by 405.69 kJ/mol. SO2 evolution from CO2-assisted pyrite oxidation includes different elementary reaction steps: CO2 adsorption, CO2 decomposition, CO desorption, SO2 formation, SO2 desorption, and O replenishment. CO2 decomposition is regarded as the rate-limiting step of SO2 evolution. S vacancy produced from surface lattice sulfur consumption can be replenished by the active oxygen atoms from CO2 decomposition. Compared with COS formation pathway, sulfur evolution of CO2-assisted pyrite oxidation prefers SO2 formation pathway. The proposed reaction network can be used to better understand the CO2-mediated sulfur evolution chemistry of pyrite oxidation.

Experimental study on fouling and slagging behaviors during oxy-fuel combustion of high-sodium coal using a high-temperature drop-tube furnace

Zhundong coalfield occupies an important position in Chinese energy resource. However, the high-sodium content has become the hindrance for the safe use of Zhundong coal, leading to severe fouling and slagging issues. Oxy-fuel combustion is a clean combustion technology and beneficial for capturing CO2. The fouling/slagging mechanisms of Zhundong coal in oxy-fuel combustion were ambiguous and the influences of oxygen content on the slagging behaviors of high-sodium coal have yet to be fully understood. This work employed a drop-tube furnace to explore the effects of flue gas temperature and oxygen content on the fouling and slagging characteristics in oxy-fuel atmosphere, and also conducted the comparison between oxy-fuel and air cases, with the elaboration of mineral constituents, morphologies, and elemental compositions of the deposits. Experimental results showed that the fouling of the high-sodium coal worsened as the flue gas temperature rose from 900 °C to 1200 °C. The element and mineral categories of the slag were similar but the relative contents of the mineral were different between oxy-fuel and air conditions. The diffraction peak of quartz in Wucaiwan slag during oxy-fuel combustion was weaker than that in air, while the condition of Lu’an slag was different. The high sodium content and its compounds promoted the formation of initial layer and the sticky particle surface, worsening the fouling and slagging. More comprehensive understanding of slagging mechanism could be achieved through the present work, which made sense for the optimization of combustion condition and the safe utilization of Zhundong coal.

Ash deposition during pressurized oxy-fuel combustion of Zhundong coal in a lab-scale fluidized bed

The paper presents the ash deposition behavior during pressurized oxy-fuel fluidized bed combustion (POFBC) of Zhundong coal at 0.3 MPa, which has never been reported before. Ash deposits collected from different positions (windward, leeward and vertical sides) of the probe under different atmospheres were investigated in detail. The results showed that the inside deposits, i.e. the initial deposit layers, on the different positions shared the similar composition and morphology. However, the atmosphere had a significant impact on the ash deposition behavior. The inside deposits have more regular spheres and larger size under 30% O2/70% CO2 condition than those from 21% O2/79% N2 and 21% O2/79% CO2 combustion, probably due to the intensive submicron particle coagulation. Furthermore, the particles contained in the inside deposits had higher Fe and Cl in 30% O2/70% CO2 combustion compared with that in the other two combustion modes. However, the content of S in the deposits was the highest under 21% O2/79% CO2 condition, which may be attributed to the fact that high CO2 partial pressure strengthens self-desulfurization ability of ash. In addition, S and Si contributed significantly to the compositions of the inside deposits.

Density functional theory study of the heterogenous interaction between char-bound nitrogen and CO2 during oxy-fuel coal combustion

In order to have a deep insight into the NO formation mechanism during oxy-fuel combustion, density functional theory (DFT) was used to investigate the interaction between char(N) and CO2 at molecular level. The geometric structures, orbital electron distribution properties and reaction paths were calculated and optimized. The outer orbital electron properties of char(N) and CO2 indicate that CO2 acts as the oxidizer, which tends to attract electrons from char(N) during char(N)-CO2 interaction. The geometries and Mulliken properties of three initial chemisorption intermediates indicate that char(N) may mainly undergo two oxidation/gasification paths: one is carbon atom oxidation by CO2 to form CO via initial chemisorption structure of IM1. The other is nitrogen atom combination with oxygen atom and further to be oxidized to form NO via initial chemisorption structure of IM2. The initial chemisorption reactions of CO2 on char(N) surface are exothermic reactions and take place spontaneously at the operation temperature during oxy-fuel combustion. According to the reaction energy barriers and kinetic analysis, path 1 and path 2 have the comparative probability during char(N)-CO2 interaction to produce CO and NO. Nevertheless, NO produced in path 2 will further be in-situ reduced by CO over char surface, which will lead to low NO concentration in flue gas during oxy-fuel combustion.

Effects of silicon-aluminum additives on ash mineralogy, morphology, and transformation of sodium, calcium, and iron during oxy-fuel combustion of zhundong high-alkali coal

Zhundong coalfield with super-huge reserve is the largest integrated coalfield in China, while its high content of alkali and alkaline earth metals (AAEMs) gives rise to severe slagging and fouling problems during combustion. Previous studies have been conducted on the release and transformation behaviors of the AAEMs during air combustion of Zhundong coal but with little concern on iron. However, the effects of silicon-aluminum additives on oxy-fuel combustion of high-alkali coal have been rarely evaluated yet. The present study focused on the effects of four silicon-aluminum additives (Al2O3, SiO2, kaolin and diatomite) on the chemical form transformation of sodium (Na), calcium (Ca) and iron (Fe), ash morphology and mineralogy of Zhundong high-alkali coal during oxy-fuel combustion. Experimental results showed that the silicon-aluminum additives could increase the ash yield of Zhundong coal and hinder the release of Na, Ca and Fe, while various additives had different effects on the element transformation. Almost all the additives promoted the transformation of water-soluble sodium to insoluble form during oxy-fuel combustion and the amount of insoluble sodium was increased correspondingly. The variations of sodium present in forms of hydrochloric acid-soluble and ammonium acetate-soluble were highly related to coal type. Various silicon-aluminum additives exhibited different microstructures and mineral types, and the ways of retaining AAEMs were also different. With an increase in the proportion of diatomite additive, the sodium contents of water-soluble and ammonium acetate-soluble forms declined; however, the content of sodium in form of hydrochloric acid-soluble increased at first and then decreased. This work can provide a beneficial information to promote the clean, effective and safe utilization of Zhundong coals in large-scale.

Atomistic Simulation of Coal Char Oxy-Fuel Combustion: Quantifying the Influences of CO2 to Char Reactivity

Coal oxy-fuel combustion requires CO2 dilution (recycling) to reduce the furnace temperature for material protection. This enhanced CO2 concentration reduces the O2 reaction rate while CO2 gasification contributes to the char reactivity. These conflicting influences together with a competitive behavior between O2 and CO2 complicate char O2/CO2 combustion behavior. Individually quantifying the influences accompanying the replacement of N2 with CO2 and clarifying the competitive behavior are essential for predicting the char O2/CO2 combustion rate, but this is difficult to obtain via experimental approaches. Here, a simplistic atomistic simulation investigated the char oxy-fuel combustion behavior. In simulations, the reactants (O2 and CO2) were either permitted to both react with char or permitted to have only one reactive gas with the other being a passive (nonreactive) gas to explore reactivity for individual gases in a O2/CO2 atmosphere. Thus, gasification contribution to char reactivity was isolated an...