不同负载铁基载氧体的制备与性能研究

采用溶胶凝胶法制备了负载Al2O3、ZrO2和MgAl2O4的铁基载氧体,其中活性组分含量为70%,惰性载体含量为30%。高温煅烧后的铁基载氧体中活性组分为Fe2O3,相应的惰性载体物相分别为Al2O3、ZrO2和MgAl2O4,活性组分未与惰性负载发生固相反应。采用热重分析仪对铁基载氧体的还原反应活性和循环稳定性进行了测试。结果表明,负载Al2O3的铁基载氧体的还原反应活性最高,且在7周期循环中保持着95%以上的还原转化率和氧化转化率,是理想的载氧体材料。     

化学链过程中Cu低浓度掺杂改性Fe-基载氧体反应性能：实验与理论模拟

基于热重实验(TGA)和密度泛函理论(DFT)计算,对Cu低浓度掺杂Fe2O3载氧体(Cu-Fe2O3)与H2在化学链燃烧过程中反应活性和微观分子反应机理进行研究。TGA结果显示,Cu低浓度掺杂降低Fe2O3载氧体与H2反应表观活化能Ea(从83.9 kJ/mol降低至72.3 kJ/mol),因此,低浓度Cu掺杂由于原子尺度Cu掺杂缺陷的引入的确提高了Fe2O3载氧体转化率和晶格氧释放速率。DFT计算从分子水平证实Cu低浓度掺杂改变了Fe2O3载氧体与H2反应路径,路径分析表明,Cu掺杂使Fe2O3载氧体与H2反应能垒从2.30 eV分别降低至1.81 eV(Fe原子top位反应)和1.68 eV(Cu原子top位反应),Cu掺杂的Fe-基载氧体的氢还原反应优先发生在掺杂的Cu原子位,其次为Fe原子位。此外,计算结果表明,因Cu-O和Cu-Fe键的引入,低浓度Cu掺杂改变了Fe2O3载氧体微观结构,这对于载氧体的晶格氧快速释放是有利的。     

废弃活性炭化学链气化制富氢合成气

以废弃活性炭为原料,以Fe4ATP6复合载氧体为载氧体,在间歇高温流化床中考察了废弃活性炭化学链气化制富氢合成气反应的较优条件及复合载氧体的循环反应特性。结果表明,Fe4ATP6复合载氧体具有提供晶格氧及催化气化的双重作用,显著提高了碳转化率,促进了废弃活性炭气化过程,反应活性良好。废弃活性炭化学链气化制富氢合成气的优化反应条件:900℃、水蒸气流量为0.25 g·min~(-1)、OC/C比为1。在上述条件下,碳转化率达92.15%,合成气产量达1.20 L·g~(-1),其中H2产量为1.09 L·g~(-1),平均浓度为55.30%。10次循环实验表明Fe4ATP6复合载氧体的反应活性略有降低,通过SEM、XRD分析载氧体的表面形貌、物质组成发现,载氧体反应后结构变化较大,粒径减小,生成了无反应活性的硅酸铁。     

餐厨垃圾化学链气化制备合成气

利用溶胶凝胶法制备了Cu Fe2O4/ATP(凹凸棒土,attapulgite)载氧体,选取典型的淀粉类餐厨垃圾(大米和面食类厨余物)作为气化原料,在流化床反应器中对餐厨垃圾化学链气化制合成气进行了实验研究。通过考察操作温度、水蒸气流量和O/C摩尔比(载氧体释氧摩尔量与物料含碳摩尔量之比)对气化过程的影响,得到餐厨垃圾化学链气化的较优操作条件为:850℃、水蒸气流量1.0 g·min-1、O/C摩尔比0.5。在该操作条件下,合成气产量为0.822 m3·kg-1,H2和CO的平均浓度分别为45.74%和22.24%,碳转化率达到83.57%。经十次循环实验后,Cu Fe2O4/ATP载氧体晶相结构稳定,主要以Cu Fe2O4形式存在,载氧体局部轻度烧结,但仍具有优良的循环特性。     

镍包覆Al2O3纳米颗粒对氧化铝陶瓷与铝之间润湿性的影响

采用Ni(NO3)2·6H2O前驱体液相包覆技术对纳米Al2O3颗粒进行金属化处理,经过干燥、加热分解和高温氢气还原处理后,前驱体完全转化为金属Ni晶体,从而获得镍涂覆的Al2O3颗粒。X射线衍射、透射电子显微镜和能谱分析结果表明:金属镍包覆在纳米Al2O3颗粒表面。包覆的纳米Al2O3颗粒经过热压烧结制备的陶瓷体与金属铝之间的润湿角为72.5°,明显改善了陶瓷与金属之间的润湿性。     

Al2O3/Fe纳米复合粉体的制备及其陶瓷的性能研究

以纳米α-Al2O3和Fe(NO3)3·9H2O为原料,采用非均相沉淀法制备了Fe包裹Al2O3的纳米复合粉体.经XRD、SEM分析发现:复合粉体前驱体经500 ℃焙烧,在H2中700 ℃还原可以得到纳米Fe包裹Al2O3的纳米复合粉体.粉体分散良好,Al2O3表面的纳米Fe粒子呈非连续状态,颗粒为球形,尺寸为30 nm左右,分布均匀.将复合粉体在热压下(30 MPa)烧结获得Al2O3/Fe复合陶瓷,当加入5mol%Fe时,陶瓷的热压烧结温度比单相Al2O3陶瓷降低将近100 ℃.含量为10mol%Fe的陶瓷样品在1500 ℃热压烧结后,断裂韧性可达到5.62 MPa,与相同条件下烧结的单相Al2O3陶瓷(KIc=3.57 MPa)相比提高了近57%.     

Co-Fe_2O_3纳米载氧体作用下CO化学链燃烧富集CO_2

制备了不同量级Co掺杂Fe2O3载氧体Co-Fe2O3,利用BET和TEM对载氧体结构进行表征。通过在不同温度下Co-Fe2O3与气体燃料CO的还原反应,考察Co-Fe2O3对CO化学链燃烧特性。结果表明,同一温度条件下,掺杂量越高,还原反应转化率越高;掺杂量不变的情况下,温度升高促使还原程度加深,缩短了载氧体完全还原转化的时间。根据TGA曲线进行了化学动力学分析,发现Co0.2Fe还原反应过程在344.7~391.0℃和414.7~472.5℃温度范围反应动力学对应扩散控制的Jander方程模型,607.6~681.5℃温度范围对应二维扩散反应模型,并分别计算出相应模型的表观活化能和频率因子。结果可为化学链燃烧技术应用提供理论指导。     

颗粒粒度对Cu基载氧体反应性能的影响

基于化学链燃烧新流程,采用固定床反应器研究了Cu基载氧体粒度、作为活性组分的Cu粉粒度及作为惰性载体的g-Al2O3粒度对载氧体反应性能的影响. 结果表明,载氧体的还原率及氧化率随Cu粉粒度减小而增大,Cu粉平均粒度小于63 mm时,载氧体还原率和氧化率达95%和93%以上. 载氧体还原过程中有少量CH4生成,生成量随Cu粉粒度减小而减少,Cu粉平均粒度小于32 mm时低于1%;当载氧体粒度接近g-Al2O3粒度时,载氧体的性能明显降低,只有g-Al2O3粒度明显小于载氧体粒度时,g-Al2O3才能起到分散活性组分、抑制活性组分烧结的作用.     

基于新型化学链燃烧工艺的Cu基载氧体循环寿命

采用机械混合法制备了Cu-Ni/Al2O3载氧体,并基于新型化学链燃烧工艺对其循环性能进行测试. 结果表明,Cu-Ni/Al2O3的初期反应性能良好,但随循环次数增加氧化率迅速降低,从初期的91.0%降至循环120次时的27.7%,而还原率则衰减轻微,循环120次仍维持在86.8%. 载氧体循环性能的衰减主要是颗粒粉化和粉化后细微颗粒团聚引起的,重新造粒可使其循环性能恢复到接近初期水平.     

溶胶-凝胶法制备Ni0.7Zn0.3Fe2O4镍锌铁氧体及其电磁损耗性能研究

以Zn(NO3)2·6H2O、Ni(NO3)2·6H2O和Fe(NO3)3·9H2O及柠檬酸为原料,采用溶胶-凝胶法制备前驱体,在1200 ℃下煅烧3h合成了Ni0.7Zn0.3Fe2O4铁氧体.通过TG/SDTA对前驱体进行了分析,发现柠檬酸在240 ℃附近开始分解,450～550 ℃存在柠檬酸的二次分解.利用XRD、IR和TEM对产品进行了表征,结果表明:Ni0.7Zn0.3Fe2O4属于立方晶系尖晶石结构,结晶完整,在580 cm-1附近具有铁氧体的红外吸收特征峰;由SEM观察表明,样品呈松散多孔状,由较小粒子组成;由TEM分析表明,晶粒大小在100 nm左右.在0.2～1.8 GHz的频率下对产品进行了电磁损耗性能测试,结果表明:在该频率范围内Ni0.7Zn0.3Fe2O4具有优良的电磁损耗特性,是一种良好的吸波材料.     

The kinetic rate of combustion of electrode carbon in the temperature range of 1000-1200 k

Kinetic rates of combustion of electrode carbon particles were measured in a temperature range of 1000-1200 K. Spherical carbon particles of size 7-9 mm are burnt in hot streams of nitrogen-oxygen mixtures. The velocity and the temperature of the mixture were varied. To compensate for the mass transfer resistance to the flow of oxygen to the carbon surface a mass transfer experiment was carried out in the same apparatus. By using mass transfer coefficients from the above experiment kinetic rates are analysed statistically to give the following Arrhenius type correlation of the kinetic rate: where n is in the range of 0.3 to 0.5.     

先进的低污染煤粉燃烧技术

本文分析了先进的煤粉燃烧技术应该具有的多种效能，即安全可靠、不结渣、燃烧稳定；具有低ＮＯ＿ｘ燃烧性能；有利于降低ＳＯ＿２的排放。论证了在我国研究开发低ＮＯ＿ｘ煤粉燃烧技术和推广应用不需耗费大量资金，却可大幅度减少ＮＯ＿ｘ的污染。还论证了先进的煤粉燃烧技术应采用炉内喷钙并附加增湿技术或排烟循环流化床脱硫技术。     

Devolatilization and char burning of coal particles in a fluidized bed combustor

Devolatilization and char burning were studied in an electrically heated bench-scale fluidized-bed reactor at 750 to 900°C bed temperature, gas oxygen mole fractions ranging from zero to 0.21, superficial gas velocities from 0.3 to 0.7 m/s and coal particle diameters 5 to 35 mm. The coals investigated include lignite, bituminous and anthracite. The coal devolatilization and char burning times, H/C ratio histories, and particle fragmentation were measured. Statistical correlations with the operating variables were developed for the devolatilization time. A mathematical model is given for the combustion of char. Most predictions of the model agree quite well with the experimental results.     

Transition Processes in Filtration Gas Combustion

The behavior of gas filtration combustion waves in the lowvelocity regime has been studied experimentally with variation in the parameters of the gas flow and porous medium. It is shown that in transition processes there may be quenching or formation of a stable combustionwave structure that does not correspond to the initial or final conditions. A nontrivial type of transition process accompanied by spatial transfer of the combustion zone is found.     

Homogeneous vs. catalytic combustion of lean methane—air mixtures in reverse-flow reactors

To carry out a comparative assessment of a recently proposed idea of using thermal flow-reversal reactors (TFRR) for mine ventilation air, the results for the catalytic flow-reversal reactor (CFRR) investigated within the European Project (2003) are briefly presented. Next, experimental investigations of thermal combustion are presented in this paper. These consisted of the kinetic study of homogeneous combustion in the pelletized bed and in the monolith. Kinetic equations for the two cases are derived and discussed. Experimental autothermal reverse-flow operation in a laboratory setup was performed. Due to the high heat capacity of the wall and insulation of the pelletized bed reactor, with considerable heat losses to the surroundings, autothermal operation was successful only in the monolithic reactor. It is finally concluded that the thermal combustion can be competitive compared with the catalytic oxidation.     

煤粉无焰富氧燃烧的数值模拟方法进展

无焰富氧燃烧是煤粉清洁燃烧技术的前沿发展方向之一,可在捕集高浓度CO₂的同时显著降低NOx排放,并提升富氧燃烧稳定性和热力性能。计算流体力学(CFD)作为燃烧研究的重要手段之一,具有快捷、成本低和数据丰富等优点,有效促进了无焰富氧燃烧技术发展。基于笔者团队对煤粉富氧燃烧和无焰燃烧的多年研究积累,对近十几年来煤粉无焰富氧燃烧CFD模拟方法和模拟研究进展进行了总结:首先强调了煤粉无焰燃烧的试验和数学定义,其由于存在非均相反应而区别于气体燃料无焰燃烧;然后详述了煤粉无焰富氧燃烧CFD模拟方法进展,包括模拟流动、传热、燃烧和污染物生成方面的子模型和机理,其中考虑强烈烟气卷吸的可实现k-ε湍流模型、P1或DO辐射模型及针对富氧气氛修正的WSGG气体辐射模型、CPD挥发分析出模型、考虑湍流与化学反应交互的有限速率EDC均相燃烧模型、针对无焰及富氧燃烧开发验证的均相反应机理、考虑气化反应的多步表面焦炭非均相燃尽模型、含氮化学详细反应机理氮转化模拟、动态自适应反应机理加速算法等可显著提高煤粉无焰富氧燃烧的模拟精度和计算效率。总结了煤粉无焰富氧燃烧在基准对照试验、微观反应区域分析、宏观反应特征、污染物生成及大型化锅炉概念设计方面的模拟研究情况;最后以大涡模拟、燃烧模型、高精度反应机理及动态自适应反应机理、工业应用优化等角度展望了煤粉无焰富氧燃烧CFD研究的发展方向。     

Application concepts and evaluation of small-scale catalytic combustors for natural gas

Basic application concepts of catalytic combustion are roughly classified into three types, and the development of catalysts, combustion performance and applicability are stated. On the diffusive catalytic combustion method, completeness of methane combustion and its reaction mechanism have been demonstrated by detailed combustion analysis of the burner and reaction kinetics. On the adiabatic lean premixed catalytic combustion method, applicability of a high-temperature catalyst system based on Mn-substituted hexaaluminate monolithic honeycomb to a 1.5 MW gas turbine combustor has been investigated through pressurized combustion tests and prototype engine-rig tests. As a result, a good outlook of the basic technical problems to overcome including the catalyst durability and the combustor control method was obtained, but another problem was that of the combustor capacity. In view of the progress of the non-catalytic lean premixed combustion method, it was concluded that a hybrid catalytic combustion method limiting catalytic combustion to the low-temperature range in this concept might become efficient in the future, but that it would depend on the development of efficient catalysts initiating their activity at about 350°C and having durability at 1000°C.     

Free-convective regime of flame spread over a fuel film on a substrate

Flame spread over a liquid fuel film on a thin metallic substrate under free convection was studied experimentally. Instantaneous flame velocities correlate with the flame length. The average flame velocity increases from 2 to 30–40 cm/sec with the slope angle of the substrate to the horizon varying in the range of 0–90°. For a substrate of specified width, the flame velocity is inversely proportional to the heat capacity of the unit area of the substrate-fuel system and to the differences between the temperature corresponding to the formation of a stoichiometric mixture of the saturated fuel vapor and air and the ambient temperature. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 21–30, September–October, 2007.     

Combustion limits of liquid monofuels

A mathematical model for steady-state nonadiabatic waves of filtration combustion of liquid monofuels in narrow tubes is proposed. Using this model, it is shown that combustion in this system can proceed in two regimes with different dominant mechanisms of heat transfer from combustion products to the preflame zone. The nature and parametric dependences of the limits of both regimes are analyzed. Calculations using the model are in good agreement with experimental data on the combustion of liquid hydrazine in narrow tubes. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 29–39, March–April, 2008.     

高温条件下催化剂对煤粉燃烧性能的研究

在1 000℃、缺氧条件下研究了催化助燃剂NaC1、KNO3、锰矿物质对无烟煤的燃烧率的影响.结果表明：复配不同催化助燃剂比例的复合添加剂1#、2#、3#,KNO3的催化效果好于NaCl和锰矿物质,复合添加剂的催化效果1 #＞3#＞2#;随着添加剂量的增加,燃烧率在添加量1％处出现了拐点.