Oxidation Kinetics of Aluminum Powders in a Gas Fluidized Bed Reactor in the Potential Application of Surge Arresting Materials

In this technical paper, the oxidation mechanism and kinetics of aluminum powders are discussed in great details. The potential applications of spherical aluminum powders after oxidation to be part of the surging arresting materials are discussed. Theoretical calculations of oxidation of spherical aluminum powders in a typical gas fluidization bed are demonstrated. Computer software written by the author is used to carry out the basic calculations of important parameters of a gas fluidization bed at different temperatures. A mathematical model of the dynamic system in a gas fluidization bed is developed and the analytical solution is obtained. The mathematical model can be used to estimate aluminum oxide thickness at a defined temperature. The mathematical model created in this study is evaluated and confirmed consistently with the experimental results on a gas fluidization bed. Detail technical discussion of the oxidation mechanism of aluminum is carried out. The mathematical deviations of the mathematical modeling have demonstrated in great details. This mathematical model developed in this study and validated with experimental results can bring a great value for the quantitative analysis of a gas fluidization bed in general from a theoretical point of view. It can be applied for the oxidation not only for aluminum spherical powders, but also for other spherical metal powders. The mathematical model developed can further enhance the applications of gas fluidization technology. In addition to the development of mathematical modeling of a gas fluidization bed reactor, the formation of oxide film through diffusion on both planar and spherical aluminum surfaces is analyzed through a thorough mathematical deviation using diffusion theory and Laplace transformation. The dominant defects and their impact to oxidation of aluminum are also discussed in detail. The well-controlled oxidation film on spherical metal powders such as aluminum and other metal spherical powders can potentially become an important part of switch devices of surge arresting materials, in general.

Effect of porosity on hydrogenation kinetics of Mg-3Ni-2MnO_2 nanocomposite powder reaction bed

Hydrided Mg-3Ni-2MnO2 composite powders were fabricated by reactive ball milling with hydrogen, and accumulative hydrogenation kinetics and temperature field of reaction bed with various porosities (0.37, 0.53 and 0.63) were measured. The results show that the accumulative hydrogenation kinetics of Mg-3Ni-2MnO2 powder reaction bed depends strongly on the effect of heat transfer, mass transfer and intrinsic reaction together. The reaction bed with the porosity of 0.53 exhibits the largest hydrogenation rate. During the hydrogenation process, the temperature of reaction bed rises quickly due to the fast release of heat, and the temperature difference between center and wall with 0.53 porosity can keep high even for a long time, which promotes fast heat transfer. The further analysis indicates that more emphases should be put on heat transfer rate rather than the only improvement of the effective thermal conductivity.

Effect of the Design Parameters on the Performance of Inner-Recycling Continuous Sand Filter

A novel integrated water treatment facility, inner-recycling continuous sand filter, is discussed. The theory of micro-flocculation is applied in the sand-washing circulation system with continuous filtration and backwashing. The design and operation parameters, which affect the performance of the filter, are discussed. The key design parameters are provided as follows: diameter of filter material is 0.7 to 1.0 mm, depth of filter bed is 0.6 m, filtration velocity is less than 12 m/h, ratio of gas to water is 9:11 and sand recycling rate is 2 to 4 mm/min.

Modeling of hydrodynamics in a bubbling fluidized-bed gasifier and evaluation of the inter-phase gas exchange rate under different operating conditions

A fluid dynamic model of a bubbling fluidized-bed coal gasifier is presented considering two-phase theory of fluidization. The effects of the gasifier temperature and bed particle size on the hydrodynamic char- acteristics of both the bubble and emulsion phases of the gasifier bed are studied. The bubble diameter, bubble velocity, and bubble area fraction are evaluated for the bubble phase, whereas the gas velocity and porosity are studied for the emulsion phase, along the height of the bed. Finally, the rate of inter-phase gas exchange from the emulsion phase to bubble phase is calculated under different operating conditions.

中国纺织外贸企业面临的多重冲击及应对策略

随着近年来国际贸易环境的变化和国际市场竞争的加剧,中国纺织外贸企业面临诸多困境和挑战,如原料成本增大、汇率波动起伏、国际船运紧张、市场需求不稳定等。但各种稳外贸措施的出台、对东盟及“一带一路”沿线各国进出口贸易的持续增长、海外仓及多式联运货运方式的发展也给中国纺织外贸企业带来新机遇。鉴于此,政府应加强对纺织行业的规范管理,建立解决贸易壁垒的专门机构,中国纺织外贸企业要建数字外贸平台、树品牌形象、开拓多元市场、利用好海外营商环境等,多措并举,才能转危为机,更好地在全球纺织行业站稳脚跟。

凌钢1^(#)烧结机提高烧结矿转鼓强度生产实践

介绍了2021年以来凌钢第二炼铁厂1^(#)烧结机为了提高烧结矿转鼓强度而进行的系列生产实践。结果表明,采用厚料层烧结、实行生产参数标准化控制、强化热风烧结作用、提高混合料布料精度、提高机前混合料温度等措施可有效提高烧结矿转鼓强度,满足高炉的生产需要。

Experimental Study on the Effect of Bed Material Amount and Fuel Particle Size on Load Change of Circulating Fluidized Bed

The large-scale integration of new energy generation has put forward higher requirements for the peak-shaving capability of thermal power.The circulating fluidized bed(CFB)depends on the advantages of a wide load adjustment range and low cost of pollutant control to become a good peak shaving power supply.However,the large delay and inertia caused by its unique combustion mode make it very difficult to change the load quickly.To further understand the factors that affect the load change of CFB,and explore the method of increasing CFB load change rate,the load change experiment on the combustion side was carried out in the 0.1 MW CFB experiment platform.The influence law of bed material amount and fuel particle size on load change of CFB combustion side was revealed for the first time.The results indicated that the increase of bed material amount was beneficial to improve the load change rate on the combustion side of CFB and reduce the carbon content of fly ash,but had no obvious effect on NO_(x)emission.When the bed height at rest increased from 200 mm to 400 mm,the load change rate of the CFB combustion side load from 50%to 75%increased from 0.78%/min to 1.14%/min,and the carbon content of fly ash at 75%load decreased from 26.6%to 24.9%.In addition,the reduction of fuel particle size positively improved the load change rate on the combustion side of the CFB and reduced NO_(x)emission but had a negative effect on reducing the carbon content of fly ash.When the fuel particle size decreased from 0-1 mm to 0-0.12 mm,the load change rate of CFB combustion side load from 50%to 75%increased from 0.78%/min to 1.09%/min,and the NO_(x)emission and carbon content of fly ash at 75%load decreased from 349.5 mg/m^(3)to 194.1 mg/m^(3)and increased from 26.6%to 31.8%,respectively.

对硫酸装置二氧化硫转化系统设计的初探

当进转化器气体中φ(SO_(2))<5.5%时,不建议采用二转二吸工艺。模拟了进转化器气体中不同的二氧化硫浓度下需采用“3+2”转化工艺的临界氧含量。对转化换热流程的选取进行了分析,指出当进转化器气体中φ(SO_(2))≤6.5%时,建议采用ⅣⅠ-ⅢⅡ换热流程,并指出了该流程的缺点。建议对含一氧化碳的二氧化硫气体进行转化计算时,考虑65%左右的一氧化碳在一段床层发生转化。提出了转化器催化剂床层进气温度选择的原则及方法,针对转化设备、管道的设计选材和转化系统散热量的选取等问题进行了探讨。

冲积河流长距离冲刷不平衡输沙过程初步研究

本文从悬移质扩散方程出发 ,研究冲积河流长距离冲刷不平衡输沙过程 .对于天然沙质河流 ,床沙均为非均匀沙 ,由于较细泥沙的冲刷率总大于较粗泥沙 ,因此在床面薄层内泥沙随冲刷迅速粗化 ,致使挟沙力降低 ,不平衡输沙距离比均匀沙情况大大延长 .文中同时提出了表层床沙粗化的概化计算模式及床沙交换速率计算公式 .床沙交换速率的大小是决定含沙量恢复饱和距离的重要因素 .本文对不同类型底部边界条件进行了计算比较 ,并与黄河下游的实际冲刷资料进行了对比 ,结果表明 ,应用梯度型底部边界条件 ,且在考虑表层床沙粗化中以作者提出的公式计算床沙交换速率 。

河流冲刷过程中表层床沙粗化对不平衡输沙的影响

在分析前人的不平衡输沙研究成果的基础上 ,针对非均匀沙河床 ,提出了床沙交换速率的新物理概念 ,计算研究了不同床沙交换速率时表层床沙的粗化过程及非均匀沙含沙量恢复饱和过程。研究表明 ,由于较细泥沙的冲刷率总大于较粗泥沙 ,因此在床面薄层内泥沙随冲刷迅速粗化 ,致使挟沙力降低 ,不平衡输沙距离较均匀沙情况大大延长。床沙交换速率愈慢 ,则冲刷距离愈长。

细颗粒对粗颗粒床沙质输沙率影响的初步研究

考虑高含沙紊流涡团中细颗粒絮凝形成网络结构对粗颗粒运动影响后 ,建立了粗颗粒悬移质泥沙的输沙率计算方法。该方法中包含的细颗粒影响项反映了流域因素对粗颗粒泥沙输沙的影响 ,证明细颗粒的影响是引起多沙河流中“多来多排”现象的一个重要因素。与黄河实测资料的对比表明 ,该计算方法能够反映高含沙紊流输沙时随流域细颗粒增多粗颗粒悬移质输沙率相对增大的现象 。

循环流化床布风方式对颗粒循环流率的影响

在带中心提升管的内循环流化床冷态试验台上,针对锥形和平板形2种布风板布置方式下各控制参数对循环流率的影响进行了试验研究.结果表明:锥形布风板上的临界全部流化速度明显大于物料临界流化速度;随着气化室和提升管内风速的增加,循环流率增大,但增大的速率逐渐降低;气化室和提升管内风速以及料层高度对锥形布风板下循环流率的影响大于平板形布风板,但是物料粒径对锥形布风板循环流化床循环流率的影响却小于平板形布风板.

冲积河流混合活动层内床沙级配变化的动力学基本方程

本文将冲积河流混合活动层内床沙的交换、掺混概括为表层床沙与水中运动泥沙在床面附近湍流作用下的掺混交换和混合活动层中泥沙在沙波运动作用下的掺混交换过程,建立了冲积河流混合活动层内床沙级配变化的基本方程。该方程定量地反映了水流强度、床面沙波运动及河床冲淤变化与床沙级配变化的关系,描述了河床冲淤过程中床沙级配时空变化的动力学特性。文中还应用该方程,分析了河床冲刷粗化现象。

清水冲刷推移质输沙率变化规律

分析恒定清水冲刷水槽试验资料发现,推移质输沙率变化可分为两个阶段,即时均稳定阶段和衰减阶段。通过机理分析,建立了该两个阶段的计算公式,计算结果与试验资料吻合良好。该式可用来估算任一河段及任一时刻推移质输沙量及冲刷剖面。

钻井液对煤层气井壁稳定性影响实验研究

在对煤层气储层岩石组成及理化性能分析的基础上,通过测定煤岩与钻井液接触后的力学性质,研究各种理化性能对煤层井壁稳定性的影响。研究结果表明,钻井液侵入煤层后容易引起黏土膨胀,煤层气储层存在由于水敏引起的煤层井壁失稳的危险;在岩石强度大、无水敏的煤储层可采用清水钻进,在水敏性强的储层应在钻井液中加入黏土抑制剂,并采用欠平衡等钻井方式,控制钻井液侵入。

裤衩型循环流化床动态数学模型研究

在两段循环流化床动态仿真模型的基础上,通过考虑裤衩腿循环流化床两侧炉膛间风量和物料的横向交换对流化床动态特性的影响,建立了裤衩腿型循环流化床的动态数学模型.利用计算流体力学软件对冷态的裤衩腿循环流化床内的风烟流动进行了模拟,得到两侧炉膛给风量不一致时横向风量交换量的计算方法.重点分析了横向气体交换量、物料交换量与两侧炉膛给风量之间的相互关系,建立了裤衩腿型循环流化床内横向物料流量与横向气体流量之间的关系式.将模拟得到的床料压降与床温的变化与实际"翻床"过程中的变化进行了比较,结果表明:模型结果能够正确反映裤衩腿循环流化床的"翻床"过程.

黄河下游河道悬移质泥沙与床沙交换计算研究

在前人研究成果的基础上,根据挟沙水流任一粒径组泥沙在输移过程中质量守恒原理,建立了一维非恒定挟沙水流悬移质泥沙和床沙交换基本方程;通过引入平衡冲淤物粒径的概念,建立了河床处于淤积与冲刷时冲淤物粒径的计算公式,并提出了一套完整的一维非恒定挟沙水流悬移质泥沙和床沙交换计算方法。将该成果引入黄河下游一维扩展泥沙数学模型中,采用黄河下游1977年高含沙洪水与1999年汛后至2002年汛前冲刷系列进行了验证。结果表明,该方法能较好地模拟悬沙与床沙的交换过程,克服分组挟沙力方法的缺陷,使得非均匀沙计算理论上更加完善,应用上更加方便。

取热区蜂窝陶瓷几何特性对换热器取热率的影响

在实验验证数学模型有效性的基础上,数值研究了立式蜂窝陶瓷填充床内取热区蜂窝陶瓷几何特性对填充床内置换热器取热率的影响。热风从取热区下侧的蜂窝陶瓷流出后进入的取热区阻力不匹配,热风会重新分配,一部分进入换热器内置空间,与换热管外壁进行直接的对流换热,另一部分进入取热区蜂窝陶瓷将其加热后与换热管外壁进行辐射换热,取热区蜂窝陶瓷的几何结构影响取热区热风阻力不匹配程度与热风分配,最终影响到换热器取热率。计算结果表明:沿热风流动方向上取热区蜂窝陶瓷几何特性尺寸增大时,换热器取热率减小;垂直热风流动方向上取热区蜂窝陶瓷的两个几何特性尺寸增大时,内置换热器取热率呈现先增大后减小趋势。

平面二维河床变形的数值模拟

为了研究河道平面二维的河床变形问题,及由此而引起的对防洪、航运等造成的影响,本文给出了非均匀沙的平面二维全沙动床数学模型方程组,并考虑了悬移质不饱和输移、非均匀沙推移质输移及床沙级配的调整。 在求解水流泥沙运动方程时,采用控制体积法(SIMPLEC程式)及动边界技术,对水流速度场、悬移质浓度场及河床变形进行了数值模拟。该模型采用正交曲线网格来克服天然河道边界形状复杂、长宽尺度相差悬殊以及由于水位波动引起计算边界变化等困难。通过水流、泥沙运动及河床变形的计算,给出了水位、流速、悬移质含沙量及其级配、床沙级配变化以及河床各冲淤部位的变化,并用实测资料对计算结果进行了检验,检验结果表明,计算的水位、流速、涨水期的淤积过程及落水期的冲刷过程均与实测值吻合较好。

循环流化床锅炉一体化外置式换热器

大型循环流化床锅炉广泛采用各种形式的外置式换热器。传统的换热器只能实现换热器(EHE)和返料机构(loopseal)之间的物料流量的调节,此时进入EHE的物料将会全部顺次流过各个换热仓室,很难对外置床中的各种受热面的传热量进行单独调节。本文首次提出了一种全新的非机械阀式外置式换热器布置方式,通过控制流入各个换热仓室的固体物料流量,从而达到对各换热仓室中布置的受热面的换热情况进行单独调节。同时把EHE和loopseal结合在一起,保证向炉膛的返料。文中对这种一体化外置式换热器及其返料机构中的物料流动特性进行了冷态试验研究。试验结果表明,这种外置式换热器有很好的物料分流和流量控制特性。可以通过调节运行参数和结构参数来控制两个换热室、EHE和loopseal以及两个返料口之间的物料流量和比例。同时还得到了物料在换热室的流动特性。通过对可见输送分离高度的测量,提出了分配室和换热室相对隔板高度的设计方法。