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1.
This paper studied the flame propagation characteristics of heavy oil oxy-fuel combustion in ignition and stable combustion. The results showed that the ignition process could be divided into three stages: the pro-ignition, mid-ignition and end-ignition. The pro-ignition, the fire core generated and evolved into spherical; the mid-ignition, the spherical fire core gradually turn into tapered structure; the end-ignition, the flame tapered structure disappeared and turn into a relative stable columnar structure. By calculating the flame propagation velocities, we found that in the same combustion atmosphere, the flame propagation velocity in 29% O2 was higher than that in 21% O2; in the same O2 concentration, the flame propagation velocity in O2/N2 atmosphere was higher than that in O2/CO2. During the stable combustion, we observed the local flame structure extinguished, distorted and grew. 相似文献
2.
Zhiqiang Wang Ming Liu Xingxing Cheng Yusheng He Yingjie Hu Chunyuan Ma 《International Journal of Hydrogen Energy》2017,42(31):20306-20315
Oxy-fuel combustion of heavy oil can be applied to oil field steam injection boilers, allowing the utilization of both heavy oil and CO2 resources. The present study investigated the oxy-fuel combustion characteristics of heavy oil under different conditions, including the flame, temperature, and pollutant emission characteristics. The results showed that heavy oil combustion was stable at O2 concentrations of 29%, as the O2 concentration was increased, the flame began to brighten gradually, becoming shorter and thicker, while the temperature gradient became higher and the high temperature zone moved closer to the burner exit. The overall temperature and the combustion rates in O2/CO2 atmospheres were below those seen in O2/N2 atmospheres. The volume of NO emitted in the flue gas was almost unaffected by the change in O2 concentrations in atmospheres containing high concentrations of CO2, but it increased rapidly with increasing O2 concentration in O2/N2 atmospheres. 相似文献
3.
Dongdong Feng Dawei Guo Yijun Zhao Heping Tan Guozhang Chang Tianpeng Zhang Shaozeng Sun 《能源学会志》2019,92(6):1670-1682
Oxygen-fuel combustion is a promising technology for CO2 emission reduction. The high-temperature entrained flow reactor and high-temperature drop tube furnace were used to analyses the formation and O2/CO2 combustion characteristics of real-environment coal char in high-temperature oxy-fuel conditions. It proposed “inflection point standard” of high-temperature flame method for the preparation of real-environmental oxy-fuel coal char according to the flame method. The results show that the ratios of C=O/C-O and C=O/Car increase in the coal char compared with the raw coals. The trend of C=O/Car in oxy-fuel condition is opposite to that in the inert atmosphere, due to the effect of high-concentration CO2. To achieve the burnout rate similar to air combustion for coal char, with the increase of coal rank, the O2 concentration should be enhanced. The optimal O2 concentration for the oxy-fuel combustion of JC anthracite is 30%, while that of other low-rank coals could be lower than 30%. The combustion characteristic of JC anthracite is with the highest sensitivity to temperature and O2 concentration. 相似文献
4.
The ignition temperature and burnout of a semi-anthracite and a high-volatile bituminous coal were studied under oxy-fuel combustion conditions in an entrained flow reactor (EFR). The results obtained under oxy-fuel atmospheres (21%O2-79%CO2, 30%O2-70% O2 and 35%O2-65%CO2) were compared with those attained in air. The replacement of CO2 by 5, 10 and 20% of steam in the oxy-fuel combustion atmospheres was also evaluated in order to study the wet recirculation of flue gas. For the 21%O2-79%CO2 atmosphere, the results indicated that the ignition temperature was higher and the coal burnout was lower than in air. However, when the O2 concentration was increased to 30 and 35% in the oxy-fuel combustion atmosphere, the ignition temperature was lower and coal burnout was improved in comparison with air conditions. On the other hand, an increase in ignition temperature and a worsening of the coal burnout was observed when steam was added to the oxy-fuel combustion atmospheres though no relevant differences between the different steam concentrations were detected. 相似文献
5.
In order to investigate the behavior of limestone sulfation under oxy-fuel circulating fluidized bed (CFB) combustion condition, experiments were conducted in a 50 kW oxy-fuel CFB system under the O2/CO2 and air combustion conditions. A small cage, containing limestone particles, was dipped into the dense zone of the CFB combustor during the experiments. The calcination of limestone, pore structure of the product layer, and calcium conversion were studied. It was found that the increasing of temperature would promote the calcination of limestone and the high concentration of CO2 would inhibit calcination of limestone. The formation process of the product layer was completely different between the direct and indirect sulfation, while it was almost the same during the indirect sulfation under the oxy-fuel and air combustion. However, both the temperature and gas compositions played important roles in determining the pore structures of the product layer during the limestone indirect sulfation process. Under the O2/CO2 combustion condition, the calcium conversion of indirect sulfation was always higher than that of direct sulfation. The highest final calcium conversion after 60 min was found at 900 °C under the O2/CO2 combustion condition. 相似文献
6.
Muhammad Faisal Irfan Arash Arami-Niya Mohammed Harun Chakrabarti Wan Mohd. Ashri Wan Daud Muhammad Rashid Usman 《Energy》2012,37(1):665-672
Kinetics of bituminous coal and palm shells were evaluated using thermo-gravimetric analysis under different environments (N2/CO2/O2). The observed percent mass loss of biomass was higher than mass loss percentage of coal because biomass had higher reactivity and volatile matter content. Ignition temperatures of pure coal, biomass and their blends were also investigated and it was observed that biomass blends had improved ignition properties in both air and oxy-fuel environments. However, the combustion mechanism wasn’t affected. Different mixtures of CO2/O2 were also used on 10% palm shell–90% coal samples and compared with air as the reference. At the same composition of oxygen in oxy-fuel as that of simulated air, ignition temperatures were slightly higher and mass loss percentages were marginally lower. However, this difference due to heat capacities of N2 and CO2 was meager and was considered negligible. Upon increasing O2 content, lower ignition temperatures were observed. Kinetics of coal, palm shell and their blends were determined at different gas mixture compositions using Doyle’s and Coats-Redfern’s models. For both models, E was found to decrease with increasing palm shell composition in coal as well as increasing O2 concentration in oxy-fuel. However, a reverse trend was observed for the pre-exponentional factor(A). 相似文献
7.
《能源学会志》2020,93(2):508-517
The co-combustion characteristics of coal and microalgae with different blending ratios and under different atmospheres are studied by single particle combustion and thermogravimetric analysis methods. The combustion processes of coal, microalgae and their blends in the single particle combustion experiment have two stages, while the combustion process of coal in the thermogravimetric analysis experiment only has one stage. With the increasing blending ratio of microalgae, flames of volatiles and char of fuels become dimmer and smaller, and the average flame temperature decreases from about 1400 °C to about 1200 °C. The ignition delay time decreases from 200 ms to 140 ms, and the experimental ignition delay time of blended fuels is lower than the theoretical ignition delay time, which demonstrates that the synthetic effect between coal and microalgae exists. To analyze the influence of oxy-fuel atmosphere on the combustion characteristics, the air is replaced by the O2/CO2 atmosphere. The replacement decreases the luminosity, size and average temperature of flames. The average flame temperature of volatiles decreases from 1449.4 °C to 1151.2 °C, and that of char decreases from 1240.0 °C to 1213.4 °C. The replacement increases the ignition delay time of fuel from 80 ms to 100 ms. Increasing mole fraction of O2 in O2/CO2 atmosphere can offset these influences. With the increasing mole fraction of O2, flames of volatiles and char of fuels become brighter and larger, the average flame temperature increases from about 1100 °C to about 1300 °C, while the ignition delay time decreases from 100 ms to 77 ms. 相似文献
8.
Role of CO2 in the CH4 oxidation and H2 formation during fuel-rich combustion in O2/CO2 environments
The effect of CO2 reactivity on CH4 oxidation and H2 formation in fuel-rich O2/CO2 combustion where the concentrations of reactants were high was studied by a CH4 flat flame experiment, detailed chemical analysis, and a pulverized coal combustion experiment. In the CH4 flat flame experiment, the residual CH4 and formed H2 in fuel-rich O2/CO2 combustion were significantly lower than those formed in air combustion, whereas the amount of CO formed in fuel-rich O2/CO2 combustion was noticeably higher than that in air. In addition to this experiment, calculations were performed using CHEMKIN-PRO. They generally agreed with the experimental results and showed that CO2 reactivity, mainly expressed by the reaction CO2 + H → CO + OH (R1), caused the differences between air and O2/CO2 combustion under fuel-rich condition. R1 was able to advance without oxygen. And, OH radicals were more active than H radicals in the hydrocarbon oxidation in the specific temperature range. It was shown that the role of CO2 was to advance CH4 oxidation during fuel-rich O2/CO2 combustion. Under fuel-rich combustion, H2 was mainly produced when the hydrocarbon reacted with H radicals. However, the hydrocarbon also reacted with the OH radicals, leading to H2O production. In fact, these hydrocarbon reactions were competitive. With increasing H/OH ratio, H2 formed more easily; however, CO2 reactivity reduced the H/OH ratio by converting H to OH. Moreover, the OH radicals reacted with H2, whereas the H radicals did not reduce H2. It was shown that OH radicals formed by CO2 reactivity were not suitable for H2 formation. As for pulverized coal combustion, the tendencies of CH4, CO, and H2 formation in pulverized coal combustion were almost the same as those in the CH4 flat flame. 相似文献
9.
An experimental study on combustion instability is presented with focus on oxy-fuel type combustion. Oxidants composed of CO2/O2 and methane are the reactants flowing through a premixer-combustor system. The reaction starts downstream a symmetric sudden expansion and is at the origin of different instability patterns depending on oxygen concentration and Reynolds number. The analysis has been conducted through measurement of pressure, CH∗ chemiluminescence, and velocity. As far as stability is concerned, oxy-fuel combustion with oxygen concentration similar to that found in air combustion cannot be sustained, but requires at least 30% oxygen to perform in a comparable manner. Under these conditions and for the sudden expansion configuration used in this study, the instability is at low frequency and low amplitude, controlled by the flame length inside the combustion chamber. Above a threshold concentration in oxygen dependent on equivalence ratio, the flame becomes organized and concentrated in the near field. Strong thermoacoustic instability is then triggered at characteristic acoustic modes of the system. Different modes can be triggered depending on the ratio of flame speed to inlet velocity, but for all types of instability encountered, the heat release and pressure fluctuations are linked by a variation in mass-flow rate. An acoustic model of the system coupled with a time-lag-based flame model made it possible to elucidate the acoustic mode selection in the system as a function of laminar flame speed and Reynolds number. The overall work brings elements of reflection concerning the potential risk of strong pressure oscillations in future gas turbine combustors for oxy-fuel gas cycles. 相似文献
10.
The purpose of this study was to investigate the NOx formation and reduction mechanisms in staged O2/CO2 combustion and in air combustion. A flat CH4 flame doped with NH3 for fuel-N was formed over the honeycomb, and NOx formation characteristics were investigated. In addition, chemiluminescence of OH* distribution was measured, and CHEMKIN-PRO was used to investigate the detailed NOx reduction mechanism. In general, the NOx conversion ratio decreases with decreasing primary O2/CH4 ratio, whereas NH3 and HCN, which are easily converted to NOx in the presence of O2, increases rapidly. Therefore, a suitable primary O2/CH4 ratio exists in the staged combustion. Our experiments showed the primary O2/CH4 ratio, which gave the minimum fixed nitrogen compounds in O2/CO2 combustion, was lower than in air combustion. The NOx conversion ratio in O2/CO2 combustion was lower than in air combustion by 40% in suitable staged combustion. This could be explained by high CO2 concentrations in the O2/CO2 combustion. It was shown that abundant OH radicals were formed in O2/CO2 combustion through the CO2 + H → CO + OH, experimentally and numerically. OH radicals produced H and O radicals through H2 + OH → H + H2O and O2 + H → OH + O, because a mass of hydrogen source exists in the CH4 flame. O and OH radicals formed in the fuel-rich region enhanced the oxidation of NH3 and HCN. NOx formed by the oxidation of NH3 and HCN was converted to N2 because the oxidation occurred in the fuel-rich region where the NOx reduction effect was high. In fact, the oxidation of NH3 and HCN in the fuel-rich region was preferable to remaining NH3 and HCN before secondary O2 injection in the staged combustion. A significant reduction in NOx emission could be achieved by staged combustion in O2/CO2 combustion. 相似文献
11.
Oxy-fuel combustion of solid fuels 总被引:1,自引:0,他引:1
Maja B. Toftegaard Jacob Brix Peter A. Jensen Peter Glarborg Anker D. Jensen 《Progress in Energy and Combustion Science》2010
Oxy-fuel combustion is suggested as one of the possible, promising technologies for capturing CO2 from power plants. The concept of oxy-fuel combustion is removal of nitrogen from the oxidizer to carry out the combustion process in oxygen and, in most concepts, recycled flue gas to lower the flame temperature. The flue gas produced thus consists primarily of carbon dioxide and water. Much research on the different aspects of an oxy-fuel power plant has been performed during the last decade. Focus has mainly been on retrofits of existing pulverized-coal-fired power plant units. Green-field plants which provide additional options for improvement of process economics are however likewise investigated. Of particular interest is the change of the combustion process induced by the exchange of carbon dioxide and water vapor for nitrogen as diluent. This paper reviews the published knowledge on the oxy-fuel process and focuses particularly on the combustion fundamentals, i.e. flame temperatures and heat transfer, ignition and burnout, emissions, and fly ash characteristics. Knowledge is currently available regarding both an entire oxy-fuel power plant and the combustion fundamentals. However, several questions remain unanswered and more research and pilot plant testing of heat transfer profiles, emission levels, the optimum oxygen excess and inlet oxygen concentration levels, high and low-temperature fire-side corrosion, ash quality, plant operability, and models to predict NOx and SO3 formation is required. 相似文献
12.
Hey-Suk Kim Mi-Soo Shin Dong-Soon Jang Dae Keun Lee 《Applied Thermal Engineering》2010,30(6-7):616-622
The determination of proper amount of CO2 recirculation is one of the critical issues in oxy-fuel combustion technology for the reduction of CO2 emissions by the capture and sequestration of CO2 species in flue gas. The objective of this study is to determine the optimum value of O2 fraction in O2/CO2 mixture to obtain similar flame characteristics with LNG–air combustion. To this end, a systematic numerical investigation has been made in order to resolve the physical feature of LNG/O2/CO2 combustion. For this, SIMPLEC algorithm is used for the resolution of pressure velocity coupling. And for the Reynolds stresses and turbulent reaction the popular two-equation (k–ε) model by Launder and Spalding and eddy breakup model by Magnussen and Hjertager were incorporated, respectively. The radiative heat transfer is calculated from the volumetric energy loss rate from flame, considering absorption coefficient of H2O, CO2 and CO gases. A series of parametric investigation has been made as function of oxidizer type, O2 fraction and fuel type for the resolution of combustion characteristics such as flame temperature, turbulent mixing and species concentration. Further the increased effect of CO2 species on the flame temperature is carefully examined by the consideration of change of specific heat and radiation effect. Based on this study, it was observed that the same mass flow rate of CO2 with N2 appears as the most adequate value for the amount of CO2 recirculation for LNG fuel since the lower Cp value for the CO2 relative to N2 species at lower temperatures cancels the effect of the higher Cp value at higher temperatures over the range of flame temperatures present in this study. However, for the fuel with high C/H ratio, for example of coal, the reduced amount of CO2 recirculation is recommended in order to compensate the increased radiation heat loss. In general, the calculation results were physically acceptable and consistent with reported data in literature. Further work is strongly recommended for a large-scale combustor such as coal-fired power plant to figure out important parameters caused by the effect of increased combustor size and the presence of particle phase, etc. 相似文献
13.
Ponnuthurai Gokulakrishnan Casey C. Fuller Michael S. Klassen Richard G. Joklik Yash N. Kochar Sarah N. Vaden Timothy C. Lieuwen Jerry M. Seitzman 《Combustion and Flame》2014
The chemical species composition of a vitiated oxidizer stream can significantly affect the combustion processes that occur in many propulsion and power generation systems. Experiments were performed to investigate the chemical kinetic effects of vitiation on ignition and flame propagation of hydrocarbon fuels using propane. Atmospheric-pressure flow reactor experiments were performed to investigate the effect of NOx on propane ignition delay time at varying O2 levels (14–21 mol%) and varying equivalence ratios (0.5–1.5) with reactor temperatures of 875 K and 917 K. Laminar flame speed measurements were obtained using a Bunsen burner facility to investigate the effect of CO2 dilution on flame propagation at an inlet temperature of 650 K. Experimental and modeling results show that small amounts of NO can significantly reduce the ignition delay time of propane in the low- and intermediate-temperature regimes. For example, 755 ppmv NOx in the vitiated stream reduced the ignition delay time of a stoichiometric propane/air mixture by 75% at 875 K. Chemical kinetic modeling shows that H-atom abstraction reaction of the fuel molecule by NO2 plays a critical role in promoting ignition in conjunction with reactions between NO and less reactive radicals such as HO2 and CH3O2 at low and intermediate temperatures. Experimental results show that the presence of 10 mol% CO2 in the vitiated air reduces the peak laminar flame speed by up to a factor of two. Chemical kinetic effects of CO2 contribute to the reduction in flame speed by suppressing the formation of OH radicals in addition to the lower flame temperature caused by dilution. Overall, the detailed chemical kinetic mechanism developed in the current work predicts the chemical kinetic effects of vitiated species, namely NOx and CO2, on propane combustion reasonably well. Moreover, the reaction kinetic scheme also predicts the negative temperature coefficient (NTC) behavior of propane during low-temperature oxidation. 相似文献
14.
Effects of hydrogen peroxide on combustion enhancement of premixed methane/air flames 总被引:1,自引:0,他引:1
Guan-Bang Chen Yueh-Heng Li Tsarng-Sheng ChengHung-Wei Hsu Yei-Chin Chao 《International Journal of Hydrogen Energy》2011,36(23):15414-15426
Hydrogen peroxide is generally considered to be an effective combustion promoter for different fuels. The effects of hydrogen peroxide on the combustion enhancement of premixed methane/air flames are investigated numerically using the PREMIX code of Chemkin collection 3.5 with the GRI-Mech 3.0 chemical kinetic mechanisms and detailed transport properties. To study into the enhancement behavior, hydrogen peroxide is used for two different conditions: (1) as the oxidizer substituent by partial replacement of air and (2) as the oxidizer supplier by using different concentrations of H2O2. Results show that the laminar burning velocity and adiabatic flame temperature of methane flame are significantly enhanced with H2O2 addition. Besides, the addition of H2O2 increases the CH4 consumption rate and CO production rate, but reduces CO2 productions. Nevertheless, using a lower volumetric concentration of H2O2 as an oxidizer is prone to reduce CO formation. The OH concentration is increased with increasing H2O2 addition due to apparent shifting of major reaction pathways. The increase of OH concentration significantly enhances the reaction rate leading to enhanced laminar burning velocity and combustion. As to NO emission, using H2O2 as an oxidizer will never produce NO, but NO emission will increase due to enhanced flame temperature when air is partially replaced by H2O2. 相似文献
15.
《International Journal of Hydrogen Energy》2023,48(79):30909-30929
Moderate or Intense Low-oxygen Dilution (MILD) combustion of a syngas fuel under air-fuel, oxygen-enhanced, and oxy-fuel condition are numerically studied with using counterflow diffusion flame. Fuel composition, temperature of oxidant (Tox), and oxygen mole fraction (XO2) are selected as the main parameters. Fake species (FCO2) with the same CO2 physical properties is used for separation the physical and chemical effects of replacing CO2 with N2. According to the results, under the high preheating temperatures, the chemical effect of changing the oxidant composition from N2 to CO2 is the main reason of the changes in flame structure, ignition delay time (IDT) and heat release rate (HRR) while physical differences play a more prominent role in the low preheating temperature MILD combustion. In all XO2, the physical and chemical effects of replacing CO2 with N2 have almost the same role on the maximum flame temperature. The results of IDT expressed that chemical discrepancies of CO2 and N2 play a key role on IDT enhancement by increasing CO2 in the oxidant composition. The sensitivity analysis of CH2O for variations of Tox and XO2 shows that reactions R54, R56, R58, and R101 are the main responsible of lower HRR and higher IDT by moving from air-syngas to oxy-fuel MILD combustion. 相似文献
16.
Rastko Jovanovic Aleksandra Milewska Adrian Goanta 《International Journal of Heat and Mass Transfer》2011,54(4):921-931
It is expected that pulverized coal combustion will continue to play a major role in electricity generation for the foreseeable future. Oxy-fuel coal combustion is actively being investigated, as alternative to conventional pulverized-coal combustion, due to its potential to easier carbon dioxide sequestration. This paper presents experimental and numerical analysis of ignition phenomena in oxy-fuel conditions. A modification of standard sequential coal combustion model is proposed. The new model is developed following the criteria for the particle ignition mechanism as the function of surrounding conditions. The implemented model was validated based on ignition point position obtained from the drop tube facility experiments in various O2-N2 and O2-CO2 conditions. The obtained numerical results showed a much better agreement with the experimental results when compared with the simulations performed with the default FLUENT sub-models for coal particle ignition/combustion, thus enabling a quantitative determination of pulverized coal flame ignition point position using numerical analysis. 相似文献
17.
《International Journal of Hydrogen Energy》2022,47(87):37052-37071
In this work, extensive chemical kinetic modeling is performed to analyze the combustion and emissions characteristics of premixed NH3/CH4–O2/N2/H2O2 mixtures at different replacement percentages of air with hydrogen peroxide (H2O2). This work is comprehensively discusses the ignition delay time, flame speed, heat release rate, and NOx & CO emissions of premixed NH3/CH4–O2/N2/H2O2 mixtures. Important intermediate crucial radicals such as OH, HO2, HCO, and HNO effect on the above-mentioned parameters is also discussed in detail. Furthermore, correlations were obtained for the laminar flame speed, NO, and CO emissions with important radicals such as OH, HO2, HCO, and HNO. The replacement of air with H2O2 increases flame speed and decreases the ignition delay time of the mixture significantly. Also, increases the CO and NOx concentration in the products. The CO and NOx emissions can be controlled by regulating the H2O2 concentration and equivalence ratios. Air replacement with H2O2 enhances the reactions rate and concentration of intermediate radicals such as O/H, HO2, and HCO in the mixture. These intermediate radicals closely govern the combustion chemistry of the NH3/CH4– O2/N2/H2O2 mixture. A linear correlation is observed between the flame speed and peak mole fraction of OH + HO2 radicals, and 2nd degree polynomial correlation is observed for the peak mole fraction of NO and CO with HNO + OH and HCO + OH radicals, respectively. 相似文献
18.
Juan Riaza Reza Khatami Yiannis A. Levendis Lucía Álvarez María V. Gil Covadonga Pevida Fernando Rubiera José J. Pis 《Combustion and Flame》2014
A fundamental investigation has been conducted on the combustion behavior of single particles (75–150 μm) of four coals of different ranks: anthracite, semi-anthracite, medium-volatile bituminous and high-volatile bituminous. A laboratory-scale transparent laminar-flow drop-tube furnace, electrically-heated to 1400 K, was used to burn the coals. The experiments were performed in different combustion atmospheres: air (21%O2/79%N2) and four simulated dry oxy-fuel conditions: 21%O2/79%CO2, 30%O2/70%CO2, 35%O2/65%CO2 and 50%O2/50%CO2. The ignition and combustion of single particles was observed by means of three-color pyrometry and high-speed high-resolution cinematography to obtain temperature–time histories and record combustion behaviors. On the basis of the observations made with these techniques, a comprehensive examination of the ignition and combustion behaviors of these fuels was achieved. Higher rank coals (anthracite and semi-anthracite) ignited heterogeneously on the particle surface, whereas the bituminous coal particles ignited homogeneously in the gas phase. Moreover, deduced ignition temperatures increased with increasing coal rank and decreased with increasing oxygen concentrations. Strikingly disparate combustion behaviors were observed depending on the coal rank. The combustion of bituminous coal particles took place in two phases. First, volatiles evolved, ignited and burned in luminous enveloping flames. Upon extinction of these flames, the char residues ignited and burned. In contrast, the higher rank coal particles ignited and burned heterogeneously. The replacement of the background N2 gas of air with CO2 (i.e., changing from air to an oxy-fuel atmosphere) at the same oxygen mole fraction impaired the intensity of combustion. It reduced the combustion temperatures and lengthened the burnout times of the particles. Increasing the oxygen mole fraction in CO2 to 30–35% restored the intensity of combustion to that of air for all the coals studied. Volatile flame burnout times increased linearly with the volatile matter content in the coal in both air and all oxygen mole fractions in CO2. On the other hand, char burnout times increased linearly or quadratically versus carbon content in the coal, depending on the oxygen mole fraction in the background gas. 相似文献
19.
The air and oxy-fuel combustion processes of two low-grade lignite coals were investigated by thermogravimetric analysis (TGA) method. Coals were provided from two different coal mines in the Aegean region of Turkey. Oxy-fuel combustion experiments were carried out with three different gas mixtures of 21% O2–79% CO2; 40% O2–60% CO2 and 50% O2–50% CO2 at 950 °C and heating rates of 10 °C/min, 20 °C/min and 40 °C/min. The kinetics of the oxy-fuel combustion of coals were studied by using four different methods namely, Coats-Redfern (model-fitting method), Friedman (FR), Flynn–Wall–Ozawa's (FWO) and Kissinger–Akahira–Sunose's (KAS) methods. The apparent activation energies of combustion process calculated by FWO method are slightly but systematically higher than that calculated by the KAS and FR methods for the oxy-fuel atmospheres. Combustion behavior of both coals in the oxy-fuel combustion environment could vary significantly, likely due to their characteristics such ash and volatile matter contents. 相似文献
20.
Lun Ma Tingxu Wang Jichang Liu Qingyan Fang Anlong Guo Cheng Zhang Gang Chen 《能源学会志》2019,92(3):413-427
The combination of oxy-fuel and blended-coal combustion may be one of these effective methods to both reduce CO2 emissions and improve energy utilization efficiency in coal-fired power stations. The aim of this study is to investigate oxy-fuel combustion interactions of blended coals under different conditions using a thermo-gravimetric analyzer. The results show that compared with those in an O2/N2 mixture, the promotive and inhibitive effect and the comprehensive interactions are considerably weaker in an O2/CO2 mixture. In the O2/CO2 mixture, both increasing the O2 concentration and decreasing the particle size result in decreasing the promotive effect but increasing the inhibitive effect and the comprehensive interactions, which increase the non-additive combustion characteristics. Enhancement of the heating rate increases the promotive effect but decreases the inhibitive effect and the comprehensive interactions, which weaken the non-additive combustion characteristics. Of these factors, the effects of the oxygen concentration and heating rate on comprehensive interactions are greater than that of particle size. This study provides useful information for the design and optimization of thermo-chemical conversion systems of coal blends in the O2/CO2 atmosphere. 相似文献