石灰石炉内高温煅烧脱硫及产物活性的实验

以石灰石炉内喷入与烟气循环流化床的组合式燃煤锅炉烟气脱硫工艺方案为应用对象,选择辽宁地区富产的7种石灰石,在煤燃烧热态实验装置上,对其炉内煅烧高温脱硫效果及其影响因素进行了实验研究,并对煅烧产物的活性及其影响因素进行了实验研究。实验表明：煅烧温度、钙硫比、煅烧停留时间、石灰石粒度等因素对脱硫效果均有显著影响;煅烧温度、煅烧停留时间和石灰石粒度等因素对石灰石高温煅烧产物活性有显著影响;石灰石最佳煅烧温度区间为1000℃～1200℃,在此温度区间内,炉内脱硫效率最高,煅烧产物的活性最高。图7表2参2     

加压条件下石灰石同时煅烧和脱除H_2S的反应特性

基于石灰石等钙基脱硫剂在加压气化炉内可能同时发生煅烧和脱硫反应的事实,在Thermax 500型加压热重分析仪上进行了还原条件下石灰石的煅烧和脱硫过程同时进行的实验,主要研究了温度(800～900℃)和CO2分压(0～0.03,MPa)等因素的影响.结果表明:反应气体中无CO2时,石灰石煅烧和脱硫两个反应过程的影响程度与温度有关,800,℃比900,℃时更为明显;在CO2存在的条件下,石灰石的煅烧速率减缓,影响了后续脱硫过程的快速进行,而脱硫反应产物CaS的存在也严重抑制了煅烧过程的进行;在高CO2分压下,石灰石煅烧和脱硫过程之间的相互影响较大.     

石灰石分解特性及微观结构迁移规律研究

采用自建的热重分析仪进行石灰石煅烧分解的热重实验,得到了温度、煅烧气氛及粒径对石灰石分解过程的影响规律,利用扫描电镜(scanning electron microscopy,SEM)和比表面积及孔隙度分析仪重点考察了分解过程中煅烧产物微观结构的迁移变化规律。研究表明:温度是影响石灰石煅烧的关键因素,温度越高,反应越快;CO2分压和粒径的增大对石灰石分解反应有一定的抑制作用;石灰石煅烧产物比表面积和比孔容随煅烧时间的延续快速增加。超过完全分解时间继续煅烧,煅烧产物产生烧结,比表面积和比孔容减小;原始石灰石几乎为无孔形态,随着煅烧过程的进行,微孔、中孔和大孔出现,呈双峰结构分布,煅烧开始至2.5 min时段内中孔增长较多,2.5～6.5 min时段内微孔和大孔快速生成,烧结导致孔的数量减少。     

二氧化硫在石灰石脱硫剂内部的扩散特性分析

通过对克努森数的计算，判别了SO2气体在煅烧后石灰石颗粒内部的扩散形式，由于分子自由程远大于孔径，故努森扩散在孔内传质过程中起控制作用。通过对扩散系数与本征动力学反应速度系数的比较，认为SO2气体通过固体产物层的扩散，对固硫反应起控制作用。文中还讨论了温度、NaCl催化、增湿活化等因素对孔结构和扩散的影响。     

煅烧参数对钙基CO2吸收剂反应特性的影响

利用能实现等温测量的热重实验台,探讨了煅烧气氛中CO2浓度对石灰石煅烧、再碳酸化以及水蒸气对循环特性的影响。结果表明,随着煅烧气氛中CO2浓度的增加,石灰石完全分解的时间逐渐延长,但在80%浓度以下,其煅烧、碳酸化动力学特性相差不多。循环过程中,水蒸气可以提高吸收剂的活性,煅烧阶段水蒸气可以增加石灰石的分解速率,碳酸化阶段水蒸气可以提高碳酸化反应速率及CO2吸收能力。     

含钙废弃物煅烧固硫性能的热分析试验研究

利用TGA/SDTA851e热分析系统研究了含钙废弃物和石灰石煅烧、固硫反应过程,用多重速率法计算了其煅烧反应活化能.并对含钙废弃物的化学成分对其煅烧特性和固硫活性的影响进行了探讨,为进一步分析含钙废弃物的脱硫机理提供理论依据.结果表明,在相同煅烧条件下,白泥煅烧的TG曲线要比石灰石的TG曲线向低温方向偏移,盐泥和碱渣虽开始分解温度低于石灰石,但其中止分解温度却高于石灰石;一定量SiO2的存在,能使煅烧反应速度加快,煅烧活化能降低,生成CaO的活性提高,而Al2O3、Fe2O3含量较高时,会造成一定的孔堵塞或形成熔融孔,煅烧活化能增加,生成CaO的活性降低.     

石灰石煅烧/碳酸化过程中微观结构的演变特性

对石灰石煅烧/碳酸化过程中微观结构的演变特性进行了研究.结果表明:石灰石不同煅烧/碳酸化阶段产物的氮吸附/脱附等温线为Ⅳ型,并在煅烧过程和碳酸化初期存在H1型吸附滞后环;石灰石煅烧产物的比表面积和比孔容随煅烧时间的增加呈线性增加,而碳酸化产物的比表面积和比孔容随碳酸化时间的增加呈指数规律迅速衰减;石灰石完全分解产物的孔容分布曲线呈双峰结构,随着煅烧反应的进行,双峰峰值不断增大,而碳酸化反应导致峰值减小;微孔、中孔和大孔对孔容积和孔面积的增加贡献不同,微孔只对孔面积的增加有一定的贡献,而中孔和大孔对孔容积和孔面积的增加皆有较大的贡献;随着比表面积和比孔容的增大,石灰石煅烧转化率呈线性增大趋势,而CaO的碳酸化转化率呈指数衰减.     

闪蒸处理对石灰石脱硫性能的影响

在自制的固体颗粒孔径增扩仪上对石灰石进行了闪蒸改性试验,并在气流反应器上对样品进行了煅烧和脱硫试验研究。结果表明,闪蒸改性处理能够增大石灰石的孔径,而且,在石灰石孔径增扩后,孔增之间的交联性得到了提高,比表面积稍有减少。石灰石经闪蒸改性后煅烧产物CaO的孔径向大孔方向偏移,同时由于闪蒸改性使反应气体的输运性能得到了较大的改善,减少了煅烧过程中烧结的影响,从而比表面积有了大幅度增大。在相同的试验条件下,闪蒸改性后样品的脱硫效率得到了明显提高。     

石灰石的爆裂与磨耗特性研究

在小型炉下预热电加热流化床实验台上对土耳其的某石灰石的爆裂和磨耗特性进行了实验研究,煅烧温度与流化介质中CO2分压力对石灰石的爆裂有着十分重要的影响,当CO2的分压力大于石灰石分解的平衡压力时,煅烧反应将受到抑制,石灰石爆裂程度很小;当CO2的分压力小于石灰石分解的平衡压力时,煅烧反应生成的CO2的析出引起内部压力增大,爆裂加大,煅烧产物的粒径将明显小于原始石灰石的粒度,孔隙率也有较大程度的提高,这将有利于固硫反应的进行。该石灰石煅烧产物在流化床内的磨耗特性与煤灰相似,磨耗速率常数基本上符合指数衰减的时间函数。     

增压条件下石灰石固硫机理实验研究

增压燃烧条件下石灰石固硫特性研究是PFBC洁净燃烧的重点课题之一，在较高CO2分压条件下，石灰石不易发生煅烧分解，从而导致增压条件古石灰石固硫机理不同于常压燃烧条件下的固硫机理，本文在增压实验台上对增压条件下石灰石固硫特性进行了实验研究，并采用JXA－80扫描电镜对试样进行了微观检测分析，确定了固硫的媒质。     

Measurement of equivalent diffusivity during the calcination of limestone

By using the expression for equivalent diffusivity during the calcination of large particles of limestone, measurements of the weight loss and calcination time yielded the equivalent diffusivity of CO₂ in porous CaO. Eight kinds of limestone were used. The experimental results showed that the equivalent diffusivity for different limestones and different particle sizes was almost the same, provided sintering did not occur in calcination.     

超细石灰石热解的数学模拟和试验研究

采用缩核模型对超细石灰石热解进行了模拟。由于颗粒较小，模型忽略了传热对热解影响，假定石灰石热解过程由二氧化碳扩散和反应界面处反应速度决定，反应速率与反应界面处二氧化碳的压力成反比，结合热解过程中由于烧结所引起的比表面积的变化，计算热解率随温度、比表面积、粒径等变化规律以及界面处压力对热解率的影响，并由试验对计算结果进行了验证。图6表1参10     

Cyclic CO2 capture performance of carbide slag

The carbonate looping process is a promising technology for CO₂ capture. The decay of sorbents reactivity over multiple cycles is an obstacle for realizing the carbonate looping process. In this work, the reactivity and stability of carbide slag for CO₂ capture have been examined. The results show that carbide slag exhibits superior CO₂ capture performance even at severe calcination temperatures in comparison with limestones, shells, pure CaCO₃, and Ca(OH)₂. X-ray diffraction analysis shows that there is mayenite (Ca₁₂Al₁₄O₃₃) formed in the calcination step for carbide slag, which is the main reason for its high stability in the carbonate looping process.     

Hydrogen production by thermocatalytic decomposition of methane over Ni-Al and Ni-Cu-Al catalysts: Effect of calcination temperature

Thermo catalytic decomposition of methane using Ni-Al and Ni-Cu-Al catalyst prepared by fusion of the corresponding nitrates is studied. The effects of catalyst calcination temperature on the hydrogen yields and the characteristics of the carbon obtained are studied. The role of copper has been also analyzed. Whatever the calcination temperature, all the catalysts show a high and almost constant hydrogen yield without catalyst deactivation after 8 h on stream, which confirms the good performance of this kind of catalysts. The presence of copper enhances the hydrogen production and the best results were obtained using catalysts calcined at 600 °C. Cu has a strong influence on the dispersion of Ni in the catalysts and inhibits NiO from the formation of nickel aluminate even at high calcinations temperatures, which facilitates the formation of the metallic Ni active phase during the subsequent catalyst reduction step. All catalysts tested promote the formation of very long filaments of carbon a few tens of nanometers in diameter and some micrometers long. The structural properties of these carbon filaments highly depend on the presence of Cu:Ni-Cu-Al catalysts promote the formation of a well-ordered graphitic carbon while Ni-Al catalysts enhance the formation of a rather turbostratic carbon.     

Preparation of spinel LiMn2O4 by supercritical hydrothermal method with heat-treatment

利用超临界水热结合后续煅烧处理的方法制备了锂离子电池正极材料LiMn₂O₄,并详细讨论了超临界水热反应过程中反应压力、反应温度和后续处理煅烧温度对LiMn₂O₄材料晶型、颗粒形貌和电化学性能的影响。实验结果表明,LiMn₂O₄材料在400 ℃、30 MPa下反应15 min,后续经过700 ℃煅烧3 h得到的样品具有结晶度良好、颗粒分布均匀等优点。LiMn₂O₄材料制备的扣式电池表现出优异的电化学性能,0.1 C倍率下初始放电比容量为125 mA·h/g;1 C下循环50周同样表现出良好的电化学性能。     

A bone-based catalyst for biodiesel production from waste cooking oil

Biodiesel production via transesterification of waste cooking oil (WCO) with methanol using waste chicken bone-derived catalyst was investigated. The calcium carbonate content in the waste chicken bone was converted to calcium oxide (CaO) at a calcinations temperature of 800°C. The catalysts were prepared by calcination at 300–800°C for 5 h and catalyst characterization was carried out by X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) surface area measurement. CaO was used as catalyst for biodiesel production. The results of the optimization imply that the catalyst concentration of 3.0 wt%, methanol to oil ratio of 3:1, and reaction temperature of 80°C for 3 h provide the maximum values of yield in methyl ester production. Reusability of the catalyst from calcined waste chicken bone was studied for four times, with a good yield.     

A facile nonaqueous route for preparing mixed-phase TiO2 with high activity in photocatalytic hydrogen generation

A facile and simple method was developed to prepare amorphous titanium oxalate from nonaqueous reaction of tetrabutyl titanate and oxalic acid in ethanol at room temperature. This complex was converted to mixed-phase TiO₂ (anatase/rutile) by calcinations. The mixed-phase TiO₂ obtained at the optimum calcination temperature (600 °C) consisting of 67 wt% anatase and 33 wt% rutile exhibited superior photocatalytic hydrogen production activity (1026 μmol h^?1) with high stability, which can be ascribed to the phase-junctions (anatase/rutile) and high crystalline.     

On a subgrid-scale heat flux model for large eddy simulation of turbulent thermal flow

A non-linear subgrid-scale (SGS) heat flux model is introduced in large eddy simulation for turbulent thermal flows. Unlike the linear isotropic eddy diffusivity model, the proposed model accounts for the SGS heat flux in terms of the large-scale strain-rate tensor and the temperature gradients. This is equivalent to using a tensor diffusivity. The model is to some extent similar to a scale-similarity model subjected to a Taylor expansion for the filtering operation. The formulation leading to the present proposal is discussed. The model is examined in LES for a buoyant flow in an infinite vertical channel with two differentially heated side walls. It is shown that the proposed model reproduces reasonable results as compared with the isotropic SGS diffusivity model and DNS data.     

Production of syngas from carbon dioxide reforming of methane by using LaNixFe1−xO3 perovskite type catalysts

A series of bulk and supported LaNixFe1-xO3 catalysts were synthesized, characterized and studied for dry reforming of methane (DRM) reaction. The catalysts were synthesized using sol-gel, incipient wetness impregnation (IWI) and co-precipitation methods. The catalysts were characterized by BET, XRD, FE-SEM, H2-TPR, and FTIR spectroscopy. A specific type of perovskite phase was obtained while changing the ratio of Ni to Fe for the synthesis of LaNixFe1-xO3 perovskite catalyst. The addition of supports increased the dispersion of perovskite phase, surface area and pore volume of the bulk perovskite catalysts. The support silica destroyed the perovskite features of the catalysts at higher calcinations temperature. The most active catalyst was found to be 40LaNi0.75Fe0.25O3/SiO2 calcined at 973 K for the DRM reaction with ratio of CH4:CO2:N2 as 1:1:2. The highest conversion corresponded to the catalyst calcined at 1073 K. However, the highest products yields and selectivity obtained while the catalyst was calcined at 773 K for 1 h. Thus, the choice of Ni to Fe ratio, support, method of synthesis and catalyst calcination temperature were crucial factors while synthesizing and designing a perovskite catalyst for dry reforming of methane reaction.