Sulfur evolution from coal combustion in O2/CO2 mixture

O₂/CO₂ coal combustion technology is considered as one of the most promising technologies for CO₂ sequestration due to its economical advantages and technical feasibility. It is significant to study the sulfur transfer behavior of coal in O₂/CO₂ atmosphere for organizing combustion properly and controlling SO₂ emission effectively. To clarify the effect of atmosphere on the sulfur transfer behavior, thermogravimetry coupled with Fourier Transform Infrared (TG-FTIR) system was employed to study the formation behavior of sulfur-containing gas species from Xuzhou bituminous coal pyrolysis in CO₂ atmosphere compared with that in N₂ atmosphere. Also the SO₂ formation behaviors during Xuzhou bituminous coal combustion in O₂/N₂ and O₂/CO₂ atmospheres were investigated. Results show that COS is preferentially formed during the coal pyrolysis process in CO₂ atmosphere rather than in N₂ atmosphere. When temperature is above 1000 K, sulfate in the CO₂ atmosphere begins to decompose due to the reduction effect of CO, which comes from the CO₂ gasification. During coal combustion process, replacing N₂ with CO₂ enhances the SO₂ releasing rate. SO₂ emission increases first and then decreases as O₂ fraction increases in the O₂/CO₂ mixture. XPS result of the ash after combustion indicates that higher O₂ concentration elevates the sulfur retention ability of the mineral matter in the coal.     

A study of oxy-coal combustion with steam addition and biomass blending by thermogravimetric analysis

The thermal characteristics of pulverized coal have been studied under oxy-fuel combustion conditions using non-isothermal thermogravimetric analysis (TG). The atmospheres used were 21%O₂/79%N₂, 21%O₂/79%CO₂, 30%O₂/70%O₂, and 35%O₂/65%CO₂. Coal blends of coal with 10 and 20% of biomass were also studied under these atmospheres. The addition of 10 and 20% of steam was evaluated for the oxy-fuel combustion atmospheres with 21 and 30% of O₂ in order to study the effect of the wet recirculation of flue gas. The results obtained were similar for all the different rank coals and indicated that replacing N₂ by CO₂ in the combustion atmosphere with 21% of O₂ caused a slight decrease in the rate of mass loss and delayed the burning process of the coal, biomass and coal/biomass blend samples. When the O₂ concentration was increased to 30 and 35% in the oxy-fuel combustion atmosphere, the rate of mass loss increased, the burning process occurred at lower temperatures and it was shorter in duration. An increase in the rate of mass loss and a reduction in burning time and temperature were observed after the addition of steam to the oxy-fuel combustion atmosphere. No relevant differences between the 10 and 20% steam concentrations were observed.     

Effects of inert gas CO2/N2 injection on coal low-temperature oxidation characteristic: Experiments and simulations

To deeply understand the mechanism of inert gases in inhibiting coal spontaneous combustion, the effects of dry air, CO₂, and N₂ on coal spontaneous combustion were analyzed experimentally. To this end, bituminous coal prepared from Dongrong No. 2 Coal Mine was considered the research object. Based on the adsorption configuration of the oxygen-containing coal, the displacement behavior of O₂ by CO₂ /N₂ was studied using the grand canonical Monte-Carlo (GCMC) and molecular dynamics (MD) methods. The obtained results show that the injection of CO₂ and N₂ reduces the ability of spontaneous combustion of coal. It is found that among the studied gases, CO₂ has a stronger inhibition effect on coal spontaneous combustion, which increases the temperature of CO occurrence by 5℃, decreases the concentration of CO by 29.91%, and inhibits low-temperature oxidation of coal. From the microscopic point of view, CO₂ /N₂ gases can effectively displace O₂ by diffusion and occupying adsorption sites. It is found that after the injection of CO₂, the concentration of O₂ molecules increases significantly in the vacuum layer. Compared with N₂, injection of CO₂ increases the diffusion activation of O₂ by 5.89%. This indicates that the injection of an inert gas significantly reduces the oxygen absorption capacity of coal, thereby decreasing the coal-oxygen combination reaction and preventing the spontaneous combustion of coal. The performed analyses demonstrate that CO₂ outperforms N₂ in restraining the spontaneous combustion of coal.     

Fast pyrolysis of coals under N2 and CO2 atmospheres

Oxyfuel combustion represents one way for cleaner energy production using coal as combustible. The comparison between the oxycombustion and the conventional air combustion process starts with the investigation of the pyrolysis step. The aim of this contribution is to evaluate the impact of N₂ (for conventional air combustion) and CO₂ (for oxy-fuel combustion) atmospheres during pyrolysis of three different coals. The experiments are conducted in a drop tube furnace over a wide temperature range 800–1400 °C and for residence time ranging between 0.2 and 1.2 s. Coal devolatilized in N₂ and CO₂ atmospheres at low temperatures (?1200 °C) and longer residence times (>?0.5 s), the char-CO₂ reaction is clearly observed, whose intensity depends on the nature of the coal. Furthermore, the volatile yields are simulated using Kobayashi’s scheme and kinetic parameters are predicted for each coal. The char gasification under CO₂ is also accounted for by the model.

     

Investigation of the evolved gases from Sulcis coal during pyrolysis under N2 and H2 atmospheres

The evolution of gases and volatiles during Sulcis coal pyrolysis under different atmospheres (N₂ and H₂) was investigated to obtaining a clean feedstock of combustion/gasification for electric power generation. Raw coal samples were slowly heated in temperature programmed mode up to 800 °C at ambient pressure using a laboratory-scale quartz furnace coupled to a Fourier transform infrared spectrometer (FTIR) for evolved gas analysis. Under both pyrolysis and hydropyrolysis conditions the evolution of gases started at temperature as low as 100 °C and was mainly composed by CO and CO₂ as gaseous products. With increasing temperature SO₂, COS, and light aliphatic gases (CH₄ and C₂H₄) were also released. The release of SO₂ took place up to 300 °C regardless of the pyrolysis atmosphere, whilst the COS emissions were affected by the surrounding environment. Carbon oxide, CO₂, and CH₄ continuously evolved up to 800 °C, showing similar release pathways in both N₂ and H₂ atmospheres. Trace of HCNO was detected at low pyrolysis temperature solely in pure H₂ stream. Finally, the solid residues of pyrolysis (chars) were subjected to reaction with H₂ to produce CH₄ at 800 °C under 5.0 MPa pressure. The chars reactivity was found to be dependent on pyrolysis atmosphere, being the carbon conversions of 36% and 16% for charN₂ and charH₂, respectively.     

Experimental and numerical simulation of effects of CO2/N2 concentration and initial temperature on combustion characteristics of biomass syngas

Biomass syngas is a form of renewable energy with very broad application prospects, and it has different combustion characteristics according to the fuel composition and processing technology of biomass syngas. The influence of combustion composition, diluent and temperature variation on combustion characteristics were studied in this paper. The FFCM-1 mechanism was used to investigate the combustion characteristics of CO/CH₄/H₂ under varied diluents CO₂/N₂ and temperature by using spherical expansion flame method and ANSYS CHEMKIN-PRO. The experimental laminar burning velocity was compared with the simulation results of FFCM-1 mechanism. The results reveal that the experimental data are in good agreement with the simulation results, which are somewhat different under the condition of rich fuel. The laminar burning velocity decreases significantly with the increase of diluent CO₂/N₂, with the effect of diluent CO₂ being more significant. The laminar burning velocity increase dramatically with the increase of initial temperature, and the adiabatic flame temperature also decreases with the increase of diluent. The reduction caused by diluent CO₂ is much larger than that caused by diluent N₂. The change of initial temperature also affects the adiabatic flame temperature, but the range of variation is not as pronounced as that of diluent. Not only was the interaction between the combustion characteristics of CO/CH₄/H₂ under different diluents and temperature changes explored in this paper, but the influence mechanism was also revealed in depth.     

Thermodynamic equilibrium study of mineral elements evaporation in O2/CO2 recycle combustion

The facility for the analysis of chemical thermodynamics method (F*A*C*T) based on the Gibbs energy minimization principle, was used to characterize the evaporation of mineral elements of coal in O₂/CO₂ recycle combustion. The effects of atmosphere and temperature on the speciation of mineral species were discussed. The results show that Na(K)Cl(g), FeO(g), and SiO(g) are the dominant gaseous species of the mineral elements. The dominant species of mineral elements in flue gases depend on both the combustion conditions (reducing or oxidizing) and the atmosphere. In O₂/CO₂ mixture combustion, the evaporation rate of mineral elements is much lower than that in air combustion, especially under reducing atmosphere. The total evaporation of mineral elements in O₂/CO₂ atmosphere and air combustion under reducing conditions is 4.46% and 9.65% respectively, up to the temperature of 2400 K. The calculation values are consistent with the experiment values. The decrease in the mineral element evaporation is helpful to suppress the tendency to form fine particle matter and the tendency of initial ash deposition.     

TG–FTIR analysis of oxidation kinetics of some solid fuels under oxy-fuel conditions

A possible technology that can contribute reduction of carbon dioxide emission is oxy-fuel combustion of fossil fuels enabling to increase CO₂ concentration in the exhaust gas by carrying out the combustion process with oxygen and replacing air nitrogen with recycling combustion products to obtain a capture-ready CO₂ stream. The laboratory studies and pilot-scale experiments discussed during the last years have indicated that oxy-fuel combustion is a favorable option in retrofitting conventional coal firing. Estonian oil shale (OS) with its specific properties has never been studied as a fuel in oxy-fuel combustion, so, the aim of the present research was to compare thermo-oxidation of OS and some coal samples under air and oxy-fuel combustion conditions by means of thermal analysis methods. Experiments were carried out in Ar/O₂ and CO₂/O₂ atmospheres with two oil shale and two coal samples under dynamic heating conditions. FTIR analysis was applied to characterize evolved gases and emission dynamics. Kinetic parameters of oxidation were calculated using a model-free kinetic analysis approach based on differential iso-conversional methods. Comparison of the oxidation characteristics of the samples was given in both atmospheres and it was shown that the oxidation process proceeds under oxy-fuel conditions by all studied fuels with lower activation energies, however, it can last longer as the same temperatures are compared.     

Experimental and kinetic investigation of the pyrolysis,combustion, and gasification of deoiled asphalt

The pyrolysis, combustion, and gasification behaviors of deoiled asphalt were studied by a thermogravimetric analyzer and the kinetics were also analyzed using a multi-stage first-order integral model. All the experiments were conducted at non-isothermal conditions with heating rates range of 10–40 K min^?1 under N₂ (pyrolysis), air (combustion), or CO₂ (gasification) atmosphere, respectively. The results showed that, for pyrolysis, the reaction mainly occurred between 498 and 798 K and could be divided into two stages: the first was caused by the volatilization of small molecules and the second probably due to the cracking reactions. For combustion, the mass loss process could be divided into three stages: the devolatilization and oxidation first, the ignition and combustion of the volatiles second, and finally the combustion of the formed char. Under CO₂ atmosphere, the mass loss behavior was similar with that of the N₂ atmosphere at lower temperatures, but when the temperature was higher than 1,233 K, the gasification reaction obviously happened. The results of kinetic investigation showed that the multi-stage first-order integral method agreed well with the above experiments.     

Continuous high-temperature fluidized bed pyrolysis of coal in complex atmospheres: Product distribution and pyrolysis gas

This study is devoted to investigating the continuous coal pyrolysis in a laboratory fluidized bed reactor that fed coal and discharged char continuously at temperatures of 750–980 °C and in N₂-base atmospheres containing O₂, H₂, CO, CH₄ and CO₂ at varied contents. The results showed that the designed continuous pyrolysis test provided a clear understanding of the coal pyrolysis behavior in various complex atmospheres free of and with O₂. The effect of adding H₂, CO, CH₄ or CO₂ into the atmosphere on the tar yield was related to the O₂ content in the atmosphere. Without O₂ in the atmosphere, adding H₂ and CO₂ decreased the pyrolysis tar yield, but the tar yield was conversely higher with raising the CO and CH₄ contents in the atmosphere. In O₂-containing atmospheres, the influence from varying the atmospheric gas composition on the product distribution and pyrolysis gas composition was closely related to the oxidation or gasification reactions occurring to char, tar and the tested gas.     

Chemical looping combustion of high-sulfur coal with NiFe2O4-combined oxygen carrier

Chemical looping combustion (CLC) of coal has gained increasing attention as a novel combustion technology for its attractive advantage in the inherent separation of CO₂. In relative to the single metal oxide-based oxygen carrier (OC), combined OC owned superiority for CLC of coal. In this research, combined NiFe₂O₄ OC was synthesized using sol–gel combustion synthesis method, and its reaction with a typical Chinese high-sulfur coal as Liuzhi (LZ) coal was performed in a thermogravimetric analyzer (TG). And then, systematic investigation was carried out to explore the evolution of sulfur species and minerals involved in coal and their interaction with the reduced NiFe₂O₄ OC through different means, including fourier transform infrared (FTIR), field scanning electron microscopy/energy-dispersive X-ray spectrometry, X-ray diffraction, and thermodynamic simulation. TG–FTIR analysis of LZ reaction with NiFe₂O₄ indicated that two reaction stages were experienced at 350–550 and 800–900 °C, respectively, far different from LZ pyrolysis, and SO₂ occurred mainly related to oxidization of H₂S with NiFe₂O₄ over 550 °C. Meanwhile, lattice oxygen transfer rates of NiFe₂O₄ involved at the two reaction stages were higher than that of directly mixed NiO with Fe₂O₃ OC and thus more beneficial for LZ coal conversion. Both experimental means and thermodynamic simulation of the solid-reduced residues of NiFe₂O₄ with LZ coal indicated that the main-reduced counterparts of NiFe₂O₄ were Ni and Fe₃O₄. In addition, though good regeneration of the reduced NiFe₂O₄ was reached, the side products Ni₃S₂ and Ni₂SiO₄ should be noted as well for its detrimental effect on the reactivity of NiFe₂O₄ OC.     

Investigation on The Thermal Properties of Fe2O(SO4)2. Part I

The data on the thermal decomposition of FeSO₄?H₂O upon various regimes of heating and gaseous environment prove the formation of intermediate products of the types Fe₂O(SO₄)₂ and FeOHSO₄, their stability and amount being determined mainly by temperature and oxygen-reduction potential.

This communication aims at presenting results on the synthesis and characterization of Fe₂O(SO₄)₂. The synthesis was carried out using a laboratory thermal equipment operating under isothermal conditions in the temperature range 713–813 K in a gaseous environment either poor in oxygen or containing 100% oxygen. The experimental conditions under which Fe₂O(SO₄)₂ is stable are established. The effect of three basic parameters on the synthesis of Fe₂O(SO₄)₂ is clarified: the oxygen partial pressure, the ratio P_H2O/P_O2 and the temperature and the mode of heating. Mössbauer spectroscopy and X-ray diffraction data for Fe₂O(SO₄)₂ are presented.

     

Thermogravimetric analysis on gasification reactivity of Hailar lignite

Comparative studies on the Hailar lignite pyrolysis/gasification characteristics at N₂/CO₂ atmosphere and the influence of inherent mineral matters, external ash and pyrolysis temperature on its reactivity during gasification at CO₂ atmosphere were conducted by non-isothermal thermogravimetric analysis, FTIR, and X-ray diffraction (XRD) analysis. Thermogravimetric test results show that the atmosphere of N₂ or CO₂ almost has no effects on the pyrolysis behavior, and the gasification reaction under CO₂ atmosphere occurs over 943?K at the heating rate of 40?K?min^?1. The external ash prepared at 1173 and 1223?K shows a certain catalytic effect on promoting the gasification reaction, although the inherent mineral matters of Hailar lignite are found in stronger catalytic effects on gasification than the external ash. The lignite gasification reactivity decreases with increasing pyrolytic temperature between 1073 and 1273?K.     

Pyrolysis and TG Analysis of Shivee Ovoo Coal from Mongolia

The coal sample of the Shivee Ovoo deposits has been non-isothermally pyrolysed in a thermogravimetric analyser to determine the influence of temperature, heating rate and purge gas employed on the thermal degradation of the sample. The heating rates investigated in the TG were 10–50 K min^–1 to final temperature of 1000°C. N₂or CO₂ were employed as well as type of purge gas on the process of thermal degradation of the coal sample. The coal was also investigated in a fixed bed reactor to determine the influence of temperature and heating rate of the pyrolysis on the yield of products and composition of the gases evolved. The main gases produced were H₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₆ and C₃H₈ and also minor concentrations of other gases. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pyrolysis and combustion characteristics of Bio-oil from swine manure

Pyrolysis and combustion characteristics of bio-oil derived from swine manure were investigated using thermogravimetry techniques. Thermogravimetric analysis of the bio-oils were carried out in O₂ and N₂ atmosphere under different heating rates (5–20 °C/min) to a maximum temperature of 900 °C. The results indicate that the combustion processes of bio-oil occurred in three stages, namely the water and the lighter compound evaporation, i.e., the release of the volatile compounds, ignition and burning of the heavier compounds (mainly carbon), and finally decomposition of the carbonate compounds. The effect of heating rate was also studied, and higher heating rates were found to facilitate the combustion process. Different reaction kinetic mechanisms were used to treat TG data, and showed that diffusion models are the best fit for describing the combustion of bio-oil in air. The kinetic parameters of the three stages were determined using Coats–Redfern method. The study provided reliable basic data for the burning of bio-oil.     

Fe2O3/ATP载氧体制备及煤化学链燃烧性能研究

以天然凹凸棒(ATP)为载体,分别利用机械混合法、浸渍法和溶胶-凝胶法制备了3种铁基复合载氧体。利用X射线衍射(XRD)、能谱(EDS)、N₂-吸附脱附等温线等对其进行物化表征,并在900 ℃流化床中考察其煤化学链燃烧反应性能。结果表明,ATP能显著增加载氧体比表面积和抗磨损能力,并对煤转化过程有催化作用,其与Fe₂O₃的协同作用使初始碳转化速率显著提高。溶胶-凝胶法制备的U-Fe4ATP6表面Ca元素含量为4.3%,比表面积为4.920 7 m²/g,均高于其他两种载氧体,表现出更高的催化性能和反应活性:初始碳转化速率为0.168 min^-1,平均CO₂浓度为98.6%,燃烧效率为98.7%。20次反应后,U-Fe4ATP6催化性能略有降低,对应的初始碳转化速率降至0.108 min^-1,停留时间t₉₅延长到18 min;且能维持较高的反应活性,对应的CO₂捕集效率和燃烧效率分别稳定在98.6%和96.7%。     

The pyrolysis of cigarette paper under the conditions that simulate cigarette smouldering and puffing

The combustion properties and pyrolysis behavior of cigarette paper under the pyrolysis conditions of cigarette smouldering were investigated by micro-scale combustion calorimetry (MCC), thermogravimetric analysis coupled to Fourier transform infrared spectrometer (TG-FTIR), respectively. MCC results demonstrated that the combustion and pyrolysis behavior are influenced by heating rate obviously. TG-FTIR results illustrated that the composition of the gaseous products were mainly composed of CO₂, H₂O carbonyl compounds, CO, and methanol. Flash pyrolysis experiment in combination with high performance liquid chromatography (FPy-HPLC) was used to study the pyrolytic formation of eight carbonyl compounds (i.e., formaldehyde, acetaldehyde, acetone, acrolein, propionaldehyde, crotonaldehyde, methyl ethyl ketone, and butyraldehyde) during the pyrolysis of cigarette paper under the pyrolysis conditions of cigarette puffing. Moreover, the solid char formed after the flash pyrolysis experiments were studied by X-ray photoelectron spectroscopy (XPS). It had been found that the pyrolysis temperature influenced the formation of carbonyl compounds and the composition of char greatly.     

Gas-chromatographische Simultanbestimmung von O2, N2, CO,CO2, N2O,SO2, CH4, C2H4 und C2H6 im ppm-Bereich. I. Mitteilung

Zusammenfassung Die vorliegende Arbeit beschreibt ein neues Verfahren zur gas-chromatographischen Simultananalyse von N₂, O₂, CO, CO₂, N₂O, SO₂, CH₄, C₂H₄ und C₂H₆ im Konzentrations-bereich von 10% bis 10 ppm ohne Voranreicherung. Die temperaturprogrammierte Trennung der Einzelkomponenten erfolgt nach Vorsäulensplitting auf zwei parallel geschalteten Säulen. Zur Emittlung der Retentionszeiten und der Peakflächen werden zwei voneinander unabhängige Ultraschalldetektoren verwendet, deren Analogsignale nach Digitalisierung in einem Mikrocomputer verarbeitet werden. Instrumentierung und chromatographische Einzelheiten werden beschrieben und diskutiert.

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Simultaneous gas chromatographic determination of N₂, O₂, CO, CO₂, N₂O, SO₂, CH₄, C₂H₄ and C₂H₆ at the ppm-level. Part I

Summary A new procedure for the simultaneous determination of N₂, O₂, CO, CO₂, N₂O, SO₂, CH₄, C₂H₄ and C₂H₆ by gas chromatography is described. Concentrations from 10% down to 10 ppm can be determined without preconcentration. After a pre-column splitting the individual compounds of the sample are separated by a uniform temperature program on two different columns in parallel. Detection of the effluents is achieved by two individual ultrasonic detectors, the data from which are processed in a micro-computer. Instrumentation and gas chromatographic details are described and discussed.

     

Effects of additional gases on the catalytic decomposition of N2O over Cu-ZSM-5

N₂O decomposition into N₂ and O₂ was investigated in the presence of O₂, NO, CO₂, CO, CH₄, SO₂ and water vapor. Activity inhibition was observed in the presence of water vapor, and oxidant gases, whilst the reductant gases, enhanced the catalytic activity, in the temperature range of 350–550°C.     

两相流中煤粉的燃烧机理及动力学特征

利用微型流化床动力学分析仪研究了两相流条件下无烟煤粉的燃烧反应机理和动力学特征,并与热重法所得结果进行比较分析。结果表明,当温度大于850℃时,煤粉燃烧机理发生了变化,燃烧气态产物的生成比例也随之改变;当气速大于0.10 m/s时,气体扩散限制基本被消除,煤粉燃烧反应速率主要受界面化学反应控制;煤粉燃烧反应速率随着氧气分压的增大呈幂函数形式增长,且氧气分压对煤粉静置燃烧的影响更加显著。煤氧两相流燃烧的表观活化能与静置燃烧相比降低了49 kJ/mol,相同温度条件下两相流燃烧的界面化学反应阻力也明显小于热重法测试结果。