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%。     

Effective direct chemical looping coal combustion with bi-metallic Fe–Cu oxygen carriers studied using TG-MS techniques

This paper contains the results of research on a promising combustion technology known as chemical looping combustion (CLC). The noteworthy advantage of CLC is that a concentrated CO₂ stream can be obtained after water condensation without any energy penalty for CO₂ separation. The objective of this work was to prepare novel bi-metallic Fe–Cu oxygen carriers and to evaluate the performance of these carriers for the CLC process with hard coal/air. One-cycle CLC tests were conducted with supported Fe–Cu oxygen carriers in thermogravimetric analyzer (TG) utilizing hard coal as a fuel. The effects of the oxygen carrier chemical composition, particle size, and steam addition on the reaction rates were determined. The fractional reduction, fractional oxidation, and the reaction rates were calculated from the TG data. Notably, the support had a considerable effect on the reaction performance. Moreover, bi-metallic Fe–Cu oxygen carriers exhibited significantly improved reactivity compared with monometallic Fe oxygen carriers. Furthermore, the addition of a second reactive metal oxide stabilized the oxygen carrier structure. The oxidation reaction was significantly faster than the reduction reaction for all supported Fe–Cu oxygen carriers. The TG data indicated that these oxygen carriers had stable performances up to 900 °C and may be effectively used for direct coal CLC reactions.     

Characterization and evaluation of Fe2O3/Al2O3 oxygen carrier prepared by sol–gel combustion synthesis

The sol-gel combustion synthesis (SGCS) for oxygen carrier (OC) to be used in chemical looping combustion (CLC) was first designed and experimented in this work, which is a new method of OC synthesis by combining sol-gel technique and solution combustion synthesis. Cheap hydrated metal nitrates and urea were adopted as precursors to prepare Fe₂O₃/Al₂O₃ OC at the molar ratio to unity (Fe1Al1), which was characterized through various means, including Fourier transforms infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), X-ray diffractor (XRD), and N₂ isothermal adsorption/desorption method. FTIR analysis on the chemical structure of the dried gel of Fe1Al1 indicated that urea was partly hydrolyzed and the hydrated basic carbonate was formed by the combination of groups such as (Fe(_1−yAl_y)_1−xO_1−3x, CO₃²⁻ and -OH-. By analyzing the staged products during SGCS, calcination was found as a necessary step to produce Fe₂O₃/Al₂O₃ OC with separate phases of α-Fe₂O₃ and α-Al₂O₃. Through TGA-DTA, the decomposition of the dried gel was found to undergo five stages. The analysis of the evolved gases from the gel decomposition using FTIR partially confirmed the staged decomposition and assisted a better understanding of the mechanism of SGCS. XRD identification further substantiated the necessity of calcination to synthesize Fe₂O₃/Al₂O₃ OC with separate phases of α-Fe₂O₃ and α-Al₂O₃, though it was not necessary for the synthesis of single phase α-Fe₂O₃ and α-Al₂O₃. Structural characterization performed on N₂ adsorption analyzer displayed that the pore shape of Fe1Al1 particles was heterogeneous. Finally, H₂ temperature-programmed reduction (TPR) of Fe1Al1 products in TGA indicated that the reduction reaction of Fe1Al1 OC after calcination was a single step reaction from α-Fe₂O₃ to Fe, and calcination benefited to improve the transfer rate of the lattice oxygen from the OC to fuel H₂. Furthermore, four times of reduction and oxidization (redox) reaction by alternating with H₂ and air demonstrated the synthesized OC had good reactivity and sintering-resistance, much suitable to be used in the realistic CLC. Overall, the SGCS method was found superior to other existent methods to prepare Fe₂O₃/Al₂O₃ OC for CLC application.     

Cu修饰的Fe2O3/Al2O3氧载体的循环反应稳定性研究

采用冷冻干燥法制备了经Cu修饰（10%）的Fe₂O₃/Al₂O₃氧载体。利用热重分析仪分别在850、900和950 ℃等温环境下,使氧载体交替接触还原气体和氧化气体,来模拟氧载体在化学链燃烧中的循环过程。结果表明,经Cu修饰的Fe₂O₃/Al₂O₃氧载体在850和900 ℃下的等温循环过程中反应性能都很稳定,在950 ℃时的循环反应前期有微量烧结,但在循环后期反应性能也很稳定。随着反应温度的升高,氧载体氧化速率增大,还原速率和载氧率先减小后增大。与未经修饰的Fe₂O₃/Al₂O₃氧载体相比较,在900 ℃下作等温循环实验,经Cu修饰的Fe₂O₃/Al₂O₃氧载体具有较高的载氧能力和还原速率,但氧化速率较低;两者都具有较好的循环稳定性。     

Thermal characteristics of Cu-based oxygen carriers

Chemical looping combustion (CLC) is a novel combustion technology with the capability for segregation of exhaust products (i.e., carbon dioxide/H₂O or N₂/O₂). The combustion is performed in two interconnected reactors with a solid oxygen carrier circulating between them, transferring oxygen from the air to the fuel. The feasibility of a successful CLC system depends on the selection of an appropriate oxygen carrier. Cu-based oxygen carriers are good oxygen carriers due to high reactivity. However, it faces low melting point, agglomeration problems in fluidized bed. In this study, a circular reduction?Coxidation reaction simulated to the cyclic operation of the Cu-based oxygen carrier was conducted on the thermogravimetric analyzer (TG). The thermal behaviors of the potential Cu-based oxygen carrier were investigated by using an X-ray diffraction (XRD), scanning electron microscope (SEM), and surface analyzer. Multiple TG results show that the weight loss was 3.4%, indicating that the loading CuO amount was 17%. Moreover, the weight loss and weight gain was equal during 73 redox cycles, suggesting the good thermal stability of the oxygen carrier. The conversion rate of reduction and oxidation for each redox cycle remained constant even after 73 redox cycles. XRD results show the new phase formation of CuAl₂O₄ during redox cycles, which promotes the thermal stabilization of the oxygen carrier. The surface area of the oxygen carrier decreased from 105 to 13?m^2?g^?1 after 73 redox cycles and the particle size distribution shifted from 5?C15?nm to 15?C30?nm, suggesting that the micorpores were blocked or collapsed. However, the reactivity of the oxygen carrier didn??t decrease. SEM results show that CuO was evenly distributed on the surface of Al₂O₃ after 73 redox cycles. Overall, these results suggested that the Cu-based oxygen carrier was ready for fluidized bed tests.     

Preparation of copper-based oxygen carrier supported by titanium dioxide

Chemical-looping combustion (CLC) is an indirect oxygen combustion strategy, considered to be the most cost-effective power generation technology with the carbon dioxide (CO₂) inherently concentrated. The oxygen carriers in the combustion process are subjected to severe environments, such as high temperatures, multi-cycle operations, and thermodynamic limitations. Thus, the preparation of an oxygen carrier with high durability and better kinetics under harsh environments could be an essential part of the development of the CLC process. In this study, copper oxide (CuO) was selected as an active ingredient, and was supported on the titanium-dioxide-based supporting materials, which was either directly from commercial titanium dioxide powder (TiO₂) (anatase 99 %) or from tetrabutyl titanate, depending on methods. Three preparation methods were applied, including mechanic mixing (MM), sol–gel (SG), and wet impregnation (WI). Test results indicated all prepared oxygen carriers functioned properly in the multi-cycles of reduction and oxidation (redox) in thermogravimetric under 800 °C. Characterization and activity tests revealed that the CuO, prepared by the SG method was well-dispersed, highly active, and thermally stable in redox reactivity than those by the MM and WI methods. Furthermore, nucleation and diffusion models could better describe kinetics of prepared oxygen carrier based on the SG method.     

Lanthanum-promoted copper-based oxygen carriers for chemical looping combustion process

Copper-based oxygen carriers have high reactivity and favorable thermodynamic properties in the innovative chemical looping combustion (CLC), which results in the inherent capture of CO₂. The major challenge of copper-based oxygen carriers is its low melting point and potential thermal sintering and agglomeration under high-temperature cyclic CLC operations. This study is to verify the beneficial use of a rare earth metal (lanthanum) additive in copper for the enhancements of thermal stability of copper-based oxygen carriers. In both the initial 50-cycle tests using TPR-TPO techniques (temperature-programmed reduction and oxidation, 800 °C) and further extended 840-cycle tests using the micro-reactor system, in over 50 cyclic Redox TPR-TPO tests, the lanthanum-promoted copper-based oxygen carrier showed the substantial resistance to the agglomeration. Thermal analysis studies were also extended into investigations of free oxygen releasing from copper-based oxygen carrier. Characterization of used oxygen carriers revealed the significant interaction between copper and its supporting material, Al₂O₃. The Al₂O₃-supported CuO seemed to indicate a slow release of oxygen. The formation of a new crystal phase (CuAl₂O₄), combining CuO and γ-Al₂O₃, may be a major reason for the stability of copper-based oxygen carrier and the slow oxygen release under oxygen uncoupling condition. The fresh and used oxygen carriers were further characterized by (1) Brunauer–Emmett–Teller for the pore structure analysis, (2) X-ray diffraction for crystal structure analysis, and (3) scanning electron microscopy for surface analysis.     

Sewage sludge ash as an alternative low-cost oxygen carrier for chemical looping combustion

In this paper, novel low-cost oxygen carriers containing Fe₂O₃ are evaluated for use in chemical looping combustion. Sewage sludge ashes and reference samples were prepared and used in cyclic reduction and oxidation experiments in a thermogravimetric analyzer (TG). A gaseous (3 % H₂) fuel and a solid fuel (hard coal) were tested. Three-cycle CLC tests were carried out in the 600–800 °C temperature range and long-term testing was performed at 950 °C. A reactivity study showed that the natural sewage sludge ash sample was stable during the cycling TG tests when hydrogen was used as a fuel at all of the temperatures investigated. Strong temperature effects on the oxygen transport capacity were observed. An one-cycle test at 900 °C showed also that the sewage sludge ash successfully reacted with coal. The oxygen released was fully used for coal combustion, with appreciable reaction rate at temperature of ~750–800 °C, that is significantly lower than that obtained for pure Fe₂O₃-based oxygen carrier. The oxidation reaction was much faster than the reduction reaction. Moreover, the sewage sludge ash showed a low tendency toward agglomeration in the cyclic test, which was superior to the behavior of synthetic materials. The sewage sludge ash exhibited also high mechanical strength, an attrition index of 1 % and a high-temperature resistance of 1,170 °C in a reducing atmosphere. We conclude that sewage sludge ash can be effectively used as a low-cost, valuable oxygen carrier in practical application in chemical looping combustion technology for power generation.     

Perovskite ceramics and recent experimental progress in reactor design for chemical looping combustion application

Chemical looping combustion (CLC) is a novel method of carbon capture and sequestration. It facilitates CO₂ capture by lower energy penalties compared with other methods in this category. The major challenges encountered in CLC are oxygen carrier, reactor and fuel-type selection. A proper combination of these factors is required for an efficient CLC. There have been several studies with regard to oxygen carriers applicable to these processes: novel oxygen carriers, single perovskites and potential oxygen carriers, double perovskites, have been investigated for their oxygen capture and release properties in a number of studies. Different kinds of reactors have also been proposed for use in CLC processes. This paper presents information on the materials capable of oxygen storage and release and the different kinds of reactors investigated for CLC in different studies. It has been shown that, although there are several oxygen carriers and reactors with the desired function and efficiency for CLC, there remains the need for further improvement and optimisation in both areas. © 2014 Institute of Chemistry, Slovak Academy of Sciences     

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.     

CaSO4氧载体煤基合成气化学链燃烧模拟研究

相对于金属氧载体, CaSO₄作为氧载体用于化学链燃烧,具有成本低、来源广泛和氧传递容量大等诸多优点,但是气相SO₂以及各种固相硫沉积物对CaSO₄用于化学链燃烧过程造成很大的障碍。基于热力学模拟,对CaSO₄氧载体与以合成气为燃料的化学链燃烧进行了模拟研究,结果表明就CaSO₄与合成气的反应而言,在燃料反应器中, 100℃～400℃的低温反应条件下,主要发生的是合成气中CO和H₂的甲烷化反应以及硫酸盐热化学还原反应,反应产物主要是H₂S和CaCO₃;在400℃～915℃,主要发生的是CO和H₂与CaSO₄的还原反应,还原产物是CaS和CO₂;当反应温度高于915℃时,诸多副反应开始发生,反应物相除了CaS和CO₂外,CaO等副产物开始出现;而在空气反应器中,在CaS的整个氧化过程中,CaS再生形成CaSO₄的反应都是主要的,但是当空气过量系数Ф_AR<0.8时,CaSO₄与CaS的固相反应以及CaS氧化形成CaO的两个副反应也同时起作用。在燃料反应器中,最优的反应条件是反应温度915℃、常压并严格控制CaSO₄ 的加入量并确保CaSO₄氧载体过量系数Ф_FR~1;而在空气反应器中,提供充足的空气量对于CaS的氧化非常重要,空气过量系数Ф_AR ≥1不仅能确保CaS的充分氧化,而且还能避免CaS氧化过程中SO₂的排放和CaO的产生。     

Cycle performance of Cu-based oxygen carrier based on a chemical-looping combustion process

The cycle life of oxygen carrier(OC) is crucial to the practical applications of chemical looping combustion(CLC). Cycle performance of Cu/SiO_2 prepared with a mechanical mixing method was evaluated based on a CLC process characterized with an added methane steam reforming step. The Cu/SiO_2 exhibited high redox reactivity in the initial cycles, while the performance degraded with cycle number. Through characterization of the degraded Cu/SiO_2, the performance degradation was mainly caused by the secondary particles' fragmentation and the fine particles' local agglomeration, which worsened the distribution and diffusion of the reactive gases in the packed bed. A regeneration method of the degraded OC based on re-granulation has been proposed, and its mechanism has been illustrated. With this method, the performance of the degraded OC through 420 redox cycles was recovered to a level close to the initial one.     

基于赤铁矿的生物质化学链燃烧过程中氮氧化物的释放特性

在单批次进料固定床上,基于赤铁矿载氧体,研究了还原反应阶段反应温度和水蒸气量对谷壳的氮氧化物释放特性的影响。研究表明,碳转化率随反应温度升高而增加,但随水蒸气量呈先增加后下降,并在水蒸气量为1.0 g/min时达到最大值。在实验条件下,还原阶段未检测到NO₂。随着反应温度由750 ℃升高到900 ℃,NO的生成率增加,而N₂O的生成率先增加后降低,在850 ℃时达到最大值。水蒸气量由0.5 g/min升高到2.0 g/min,N₂O和NO的生成率均增加,且NO增加速率高于N₂O。在反应后的载氧体中,检测到KAlSi₃O₈存在,表明载氧体与生物质中的K元素发生反应。     

铜基载氧体与可燃固体废弃物化学链燃烧特性研究

采用机械混合法制备了铜基载氧体,利用两段式管式炉反应平台和磁悬浮热重分析仪分别研究了铜基载氧体与石墨、可燃固体废弃物典型组分及可燃固体废弃物热解气模型物CH₄的化学链燃烧特性。结果表明,机械混合法制备的Cu80Si950载氧体强度高,具有良好的转化率和循环稳定性,是实现可燃固体废弃物化学链燃烧的一种比较理想的载氧体。利用扫描电镜(SEM)、X射线衍射仪(XRD)和颗粒强度测定仪对各个反应阶段载氧体进行分析。结果表明,Cu80Si950载氧体参与反应后表面结构发生巨大改变,机械强度骤降。多次循环之后载氧体结构趋于规则均匀化,形成类似球棒形状的大孔隙率结构,强度保持不变,使得载氧体在长时间使用过程中反应性能得以维持。     

Combustion of Waste Waters Containing Organic Alkaline Salts

Abstract

The biological treatment of waste waters from chemical industry containing organic and inorganic salts causes problems because these materials inhibit the metabolic activity of the bacteria. One possible and economically feasible way to convert the organic materials into less toxic forms is a thermal oxidation process, which can take place either in a fluidized bed combustor or in a vertical combustion chamber.

The process is described and parameters of the process are discussed. Results from particle measurements on a vertical combustion chamber for the combustion of various artificial waste waters are presented. The chemical analysis of the particulate matter from different stages of the process allows a detailed characterization of the decomposition of the organic material. Conclusions are drawn both with respect to the process and the environment.     

Characterization and pyrolysis behaviour of different paper mill waste materials

Paper industry generates a considerable amount of wastes. Their composition mainly depends on the type of paper produced and the origin of cellulose fibres. Nowadays, in Spain, 40% of solid wastes generated by the paper and pulp industry are deposited directly in landfill, 25% are used in the agriculture, 13% in the ceramic industry and 7% in the concrete production. In the last years, thermal treatment methods like combustion, pyrolysis and gasification have been widely study as alternative techniques for the valorization of different organic waste materials. The main objective of the present work is to study the pyrolysis behaviour of different paper mill waste materials. For this reason, a wide characterization of eight paper mill waste materials from different origins was performed using SEM, FTIR, DRX and thermogravimetric techniques. Paper mill sludges from recycled paper, mainly wastes obtained from deinking process, showed high CaCO₃ and clays contents. Compared with the elevated total organic matter content (TOM) of paper mill waste materials their low organic carbon content determined by Cr₂O₇²⁻ oxidation reveals the elevated chemical stability of organic matter, due to high content on cellulose fibres. Analysis of samples by SEM indicates that successive recycled processes of paper leads to paper mill waste materials with more degraded fibres. XRD analyses show as crystalline cellulose was present in reject and primary sludge from paper mills that produced paper from virgin wood. However, crystalline cellulose content significantly decreased in waste materials from recycled paper. Finally, thermogravimetric analysis indicates that presence or mineral matter and degradation of cellulose significantly influences their pyrolysis behaviour. In general, weight loss of paper mill waste materials started at lower temperatures than pure cellulose. In waste materials from recycled paper weight loss continues at temperatures highest than 500 °C due to kaolinite dehydration and carbonates decomposition.     

Combustion behavior and thermal stability of ethylene-vinyl acetate composites based on CaCO3-containing oil sludge and carbon black

CaCO₃-containing oil sludge (OS) is a by-product from petroleum industry, with great amount of production. Therefore, an effective processing methods for CaCO₃-containing OS is urgently needed. Herein, ethylene-vinyl acetate (EVA) composites based on CaCO₃-containing OS and carbon black (CB) were prepared by melt blending method. The combustion behavior and thermal stability of flame-retardant EVA/OS/CB composites were investigated by cone calorimeter test, limiting oxygen index (LOI), scanning electron microscopy (SEM), smoke density test (SDT), and thermogravimetry-Fourier infrared spectrometry. The heat release rate and smoke production rate of the ternary composites containing 3% CB significantly decreased compared with the EVA/OS composites and pure EVA. Moreover, addition of a certain amount of CB could evidently increase LOI values. The morphologies and structures of the residues, revealed by SEM, ascertained that a better carbonaceous protective layer was formed on the ternary composites than the EVA/OS composite. It was obtained from SDT that CB in the material could retard the smoke production with the application of the pilot flame. The EVA/OS/CB composites assumed a higher thermal stability than the EVA/OS composites and pure EVA.

     

The sum is more than its parts: stability of MnFe oxide nanoparticles supported on oxygen-functionalized multi-walled carbon nanotubes at alternating oxygen reduction reaction and oxygen evolution reaction conditions

Successful design of reversible oxygen electrocatalysts does not only require to consider their activity towards the oxygen reduction (ORR) and the oxygen evolution reactions (OER), but also their electrochemical stability at alternating ORR and OER operating conditions, which is important for potential applications in reversible electrolyzers/fuel cells or metal/air batteries. We show that the combination of catalyst materials containing stable ORR active sites with those containing stable OER active sites may result in a stable ORR/OER catalyst if each of the active components can satisfy the current demand of their respective reaction. We compare the ORR/OER performances of oxides of Mn (stable ORR active sites), Fe (stable OER active sites), and bimetallic Mn_0.5Fe_0.5 (reversible ORR/OER catalyst) supported on oxidized multi-walled carbon nanotubes. Despite the instability of Mn and Fe oxide for the OER and the ORR, respectively, Mn_0.5Fe_0.5 exhibits high stability for both reactions.

     

Nanostructured perovskite oxides as promising substitutes of noble metals catalysts for catalytic combustion of methane

In this review, we summarize the recent development of nanostructured perovskite oxide catalysts for methane combustion, and shed some light on the rational design of high efficient nanostructured perovskite catalysts via lattice oxygen activation, lattice oxygen mobility and materials morphology engineering.     

Supercritical Fluid Extraction of Organochlorine Pesticides from Soil

Abstract

A supercritical fluid extraction (SFE) method was developed for the extraction of 21 organochlorine (OC) pesticides from soil using dichloromethane as cosolvent and magnesium sulfate as drying agent. Average recoveries of spiked OCs from six different soils generally ranged from 70 to 95%, with an average replicate precision of ± 13%. For the extraction of two soils containing “native” OCs, the SFE method gave generally similar or higher concentrations compared to Soxhlet extraction. The precision of replicate analyses of native OCs using SFE and Soxhlet extraction was ± 0.009 and ± 0.007 ug/g, with 24 and 13 degrees of freedom respectively.