流化床-化学气相沉积技术在先进核燃料制备中的应用进展

流化床-化学气相沉积（FB-CVD）技术是化工流化床技术和材料化学气相沉积制备技术的交叉耦合,兼有流化床处理量大、传热快、温度均匀以及化学气相沉积温度调节范围广、产物丰富多样等优点,其在先进核燃料制备中有着重要的应用,但随着先进核燃料“质”和“量”的不断发展要求,现有的FB-CVD技术有许多方面亟待完善。本文回顾了作者课题组利用流化床-化学气相沉积在高温气冷堆TRISO核燃料颗粒、先进核燃料包覆颗粒、核燃料示踪颗粒、基体SiC纳米颗粒、SiC@Al₂O₃复合纳米颗粒等方面的研究进展,阐述了基本方法、实验过程和典型研究结果,并分析了流化床-化学气相沉积过程中遇到的实际问题。指出了FB-CVD技术未来发展方向,主要涉及反应器规模化放大和连续性生产、孔口沉积消除及温区控制、粉体制备中的纳米颗粒连续收集、新型反应器及工艺设计等方面,具体包括高密度颗粒稳定流化放大准则、床层局部温区控制以及分区流化床结构设计等。     

基于流化床化学气相沉积的碳化硅材料制备、性能及其在核领域的应用（英文）

采用流化床化学气相沉积法(FB-CVD)制备了碳化硅包覆层,利用多尺度耦合模型对包覆过程进行了模拟,以提高包覆层的均匀性。开发了可应用在核能领域的碳化硅材料,如致密碳化硅层、细晶粒碳化硅包覆层、碳化硅/碳/硅混合包覆层、多孔碳化硅包覆层、碳化硅纳米线、碳化硅纳米粒子等。为了评估碳化硅包覆层的可靠性,进行了极端条件下的模拟事故氧化考验。对于以碳化硅为主要包覆层的燃料元件,在高通量核反应堆中进行了辐照试验,结果表明:该碳化硅包覆层材料在核应用中的表现优异。     

化学链反应器研究进展

化学链技术是目前能源技术研究的热点之一,其关键技术包括载体材料的制备和反应器的设计。综述了化学链技术的应用前景,总结了化学链反应器设计原理,回顾了目前世界上公开报道的设计完成、在建或已经运行的化学链反应器,归纳讨论了不同反应器设计细节的共同点及目的。开展以微小颗粒、纳米颗粒作为载体材料时,颗粒聚团在宏观反应器尺度下的流动传递规律、循环反应机理和系统运行控制特性的研究;开展反应器内颗粒流动-传递-反应耦合机制研究,建立多尺度统一模型;在全尺寸化学链反应器上进行系统自热实验研究;利用数值模拟方法研究和开发用于固体燃料转化过程的高效炭/灰分离器是未来化学链反应器发展需要关注的几个方面。     

流化床中包覆燃料颗粒的制备及应用

包覆燃料颗粒由燃料核芯、疏松热解炭层、内致密热解炭层、碳化硅层和外致密热解炭层组成.本工作设计建造了不同直径和结构的流化床沉积炉系统,探讨了流化床的结构、气体流量对颗粒流化状态的影响采用化学气相沉积方法生产出的包覆燃料颗粒不仅应用于我国10 MW高温气冷堆燃料元件的制备,而且探讨了包覆燃料颗粒的其它应用.     

甲醇制烯烃流化床内流化特性的多尺度CFD模拟

近些年，我国成功开发了以煤为原料的甲醇制烯烃(Methanol to Olefins, MTO)生产工艺和技术，带动煤制烯烃产业的快速发展，保障了国家能源安全。流化床式反应器是MTO工业生产的核心反应装置，通过计算流体力学(Computational Fluid Dynamics, CFD)方法深入认知MTO流化床内的流化特性规律具有重要的意义，它可以从理论上更加准确地指导MTO流化床的优化与放大。本工作采用基于宏观?亚网格层次的气泡EMMS曳力和传统TFM耦合计算的多尺度CFD方法，对工业尺度MTO流化床内的多相流化行为进行了三维数值模拟。模拟结果表明，该多尺度CFD方法考虑了气泡结构对气?固相间曳力的影响，能较准确地预测MTO流化床内轴向颗粒浓度的“S-型”分布规律，且得到实验数据的验证；所预测的径向颗粒浓度分布呈现出经典的“环?核”分布规律，气体/颗粒的轴向时均速度在径向上的分布也与实际情况相互佐证，表明该多尺度CFD方法显著改善了基于均匀曳力的传统TFM对于宏观流场的预测能力。下一步工作将多尺度CFD方法拓展应用于MTO流化床优化放大及反应特性的研究。     

化学气相沉积法制备Si/C复合负极材料的研究进展

采用化学气相沉积法制备得到的硅/碳复合材料碳层致密均匀,电化学性能好,成为目前制备该复合材料应用较多的方法。介绍了化学气相沉积法制备的硅碳复合材料的主要复合形式及电化学性能,制备过程中不同催化剂、制备条件的选择等,综述了化学气相沉积法制备硅/碳复合材料的研究进展。对化学气相沉积法在制备硅/碳复合材料的研究方向上进行了展望、提出建议。     

环流流化床反应器中乙烯气相聚合反应研究

研究开发了１种新型的用于乙烯气相聚合反应的环流流化床反应器。通过对工业Ａ催化剂和实验室自制的ＱＣＰ－０１催化剂的乙烯气相聚合反应评价及聚合物产品的颗粒形态等方面的研究,认为环流流化床反应器具有聚合反应平稳、催化剂的聚合活性高、产品粒径分布均匀等特点,是１种具有良好应用前景的新型反应器。     

新型循环流化床反应器研究进展

开发新型循环流化床反应器始终是流态化领域研究的热点。本文首先简介了循环流态化的基本原理以及床层内部流体动力学特性,然后从装置构型、操作工况、流动特性以及应用前景等方面综述了近年来新型循环流化床反应器技术的研究进展,并对其进行了系统分类:高密度循环流化床和循环湍动流化床在实现提升管增浓的基础上,极大地改善了流化床体系中明显的不均匀时空流动结构,但是各有弊端,例如高密度循环流化床(HDCFB)中颗粒沿径向混合有很大的梯度,循环湍动流化床(CTFB)中存在强烈的轴向返混以及颗粒停留时间较长,且两者整体偏低的颗粒浓度进一步限制了其在两段提升管催化裂解多产丙烯(TMP)等生产低碳烯烃工艺的应用;变径提升管反应器、内循环型提升管反应器以及多流型提升管反应器等新型反应器将提升管高效的气力输送特性与密相床内较高的颗粒浓度、高效的热质传递等优点相互耦合,在提升管内既能实现高密度输送又能形成均匀的流动结构,消除反应环境对产品分布的影响。最后指出,新型循环流化床的研究应从改善流动结构、发展优化组合技术以及建立统一流动模型3个方面着手。     

乙烯气相聚合工艺研究与技术进展

聚乙烯已成为全球产量最大、用途最广的合成材料。由于生产流程短和设备投资低的优势,流化床气相聚合工艺是聚乙烯的主要生产路线,得到了广泛而深入的研究和开发。本文综述了国内外乙烯气相聚合工艺技术的研发历程,特别是中国在气相法聚乙烯技术方面做出的重要贡献。总结了气相聚合工艺的七种操作模式,即干法气相聚合、超干法气相聚合、气相冷凝聚合、气相超冷凝聚合、气液固云雾聚合、露点聚合以及交替交变聚合。分析了各操作模式所涉及的关键科学问题和工程技术解决方案,例如反应器时空产率模型、冷凝态聚合操作点优化、溶剂的作用、黏性流化颗粒熔融温度预测、流化质量监控与声发射、多流型复合以及一器多用等,并重点介绍了气-液-固云雾聚合流化床反应器中颗粒团聚、气泡运动的新特征,云雾聚合流化床运行的新稳定机制,以及实现聚合物产品结构调控的新途径——乙烯的露点聚合和交替交变聚合技术。指出聚合反应工程学科正从聚焦传统的过程强化,发展到过程强化与产品多样化相互兼顾的变化趋势。     

流化床反应装置及硝基苯加氢的流化反应方法

<正>申请号:CN202010222841.2申请日:20200326申请人:中国石油化工股份有限公司;中国石化集团南京化学工业有限公司本发明涉及一种流化床反应装置及硝基苯加氢的流化反应方法,主要解决流化床内气固接触效率低、气泡尺寸偏大、流化质量低等问题。本发明通过在流化床反应器内部设置至少一组复合构件,使气体与催化剂颗粒在通过该构件时,破碎了气泡及颗粒团,有效提高了流化质量的技术方案,较好地解决了上述技术问题,可应用于硝基苯气相催化加氢的工业生产中。     

Carbon nanotubes produced by fluidized bed catalytic CVD: first approach of the process

Multi-walled carbon nanotubes have been produced with high yield on an iron supported catalyst by catalytic chemical vapor deposition in a fluidized bed reactor. The choice of such a technique allows to reach high selectivity towards the desired material. A remarkable feature of this process is the huge bed expansion observed during the nanotubes growth that affects the fluidization regime due to the evolution of the apparent density of the composite powder. The catalytic powder, the composite material and the purified nanotubes have been analyzed by SEM, TEM and BET nitrogen adsorption.     

A novel core-shell structured ultra-coarse WC-Co composite powders prepared by fluidized bed chemical vapor deposition

The ultra-coarse WC-Co composite powders with a core-shell structure were effectively prepared by fluidized bed chemical vapor deposition (FBCVD) using CoCl₂ precursor. An excellent interfacial bonding was formed between WC and the deposited Co. Defluidization was the major barrier to depositing high-Co-content composite powders, which was caused by the adhesion of the deposited Co particles. Decreasing the deposition temperature reduced the cohesion force of the deposited Co particles, which was thus beneficial to preventing the defluidization. Increasing the WC particle size and the gas velocity increased the collision force and benefited the fluidization. The final Co contents were largely dependent on the deposition and fluidization behaviors. For the conditions tested, the optimal deposition temperature was 800°C while the minimum WC particle size suitable for FBCVD was 25 μm.     

Plasma enhanced modification of xanthan and its use in chitosan/xanthan hydrogels

This study reports the design and construction of a fluidized bed/non‐equilibrium atmospheric‐pressure‐plasma reactor. The mechanical design of the reactor was devised to modify chemically and physically the surface of different powders. The basis for developing the design and construction of the reaction system were the non‐equilibrium atmospheric‐pressure‐plasma phenomenon known as dielectric barrier discharge and the gas‐solid bubbling fluidization. The reactor was tested modifying xanthan powder that was used in the synthesis of chitosan/xanthan hydrogels, for which the swelling capacity was measured at different pH levels. The chemical modification of xanthan was carried out in a sequential process of plasma treatment with different exposure times and gas flow (from 0.5 to 5 min), followed by chemical vapor deposition of epichlorohydrin. The swelling experiments reveal that the hydrogels increase its swelling capacity in acidic mediums and when the hydrogel was formed with xanthan with 2 or 3 min of plasma treatment. POLYM. ENG. SCI., 54:2264–2271, 2014. © 2013 Society of Plastics Engineers     

压力脉动法预测硅粉颗粒最小流化速度的实验

应用压力传感器研究了不同筛分粒径的硅粉的流化性质，证实流化床层的压力脉动标准方差σp随着表观气速的增加而线性增大, 根据σp=0的条件即可确定流化床的初始流化气速Umf. 此Umf与传统压降变化法得到的实验结果基本一致. 对测得的不同筛分粒级的硅粉的Umf进行拟合，得到了Umf与相应粒级平均粒径的关联式Umf=0.014e10(d–0.28)–0.012e–10(d–0.28)+0.065. 对双粒级复配混合颗粒体系的σp进行的实验研究发现，其σp介于相关单粒级体系的σp之间，并且粗颗粒组份的比例对σp的影响较大.     

气固两相流内中空多孔催化剂性能的数值模拟

气固流态化过程中流体和颗粒分别聚集,形成稀密两相,严重限制其传质效率和反应速率的提高。针对此问题,本工作设计了一种中空多孔结构的催化剂颗粒,通过模拟方法研究该颗粒对稀密两相气相传质与反应的影响,及其在稀密相间转换的时间尺度。结果表明,一定的流动强度时,在颗粒稀密相转换的时间尺度内,中空多孔结构的颗粒能够有效地在稀相存储反应气体,并在密相释放,为密相提供额外的反应气体,增强体系的整体反应效率。当催化反应速率高于传质速率时,在所研究的流动条件下中空多孔颗粒体系的反应效率比实心球形颗粒体系高出26.92%~29.55%。可以预见在稀密相分布更广的大型气固流化床反应器中,中空多孔结构的催化剂颗粒能够更为有效地提高反应器的整体效率。     

AlN粉末的制备方法

本文论述了AIN陶瓷粉末的三种典型制备方法—铝粉氮化法、还原氨化法和化学气相淀积法,总结了AIN粉末的生成机理以及影响AIN粉末质量的主要因素,理论分析了AIN粉末制备过程中的有关实验现象.评述了AIN粉末制备方法的优缺点,给出了大量工艺参数.     

A new CVD reactor for semiconductor film deposition

The concept and design of a new chemical vapor deposition (CVD) reactor is presented for both epitaxial and nonepitaxial film deposition in semiconductor processing. The reactor is designed in such a way that a stagnant semiconductor source fluid of uniform concentration is provided for the film deposition without causing free or forced convection. The supply of the source gas for the deposition is by diffusion through a porous material such as quartz or graphite. Compared to the low pressure CVD (LPCVD) reactor with mounted wafer configuration, the new reactor should give a better film thickness uniformity and about an order of magnitude reduction in the amount of the source gas required. Further, at least for polycrystalline silicon deposition, the deposition rate can be much higher than is currently practiced with the LPCVD reactor. Design equations for the reactor are given. Details on the design for the polycrystalline silicon deposition are also given.     

Atomic layer deposition of ZnO layers on Bi2Te3 powders: Comparison of gas fluidization and rotary reactors

Interface engineering of thermoelectric powder materials via atomic layer deposition (ALD) has attracted significant research interest owing to the dramatic improvement in energy conversion efficiency. Using ALD to uniformly coat ultrathin (a few nanometers) ZnO layers on the microscale irregular shape of bismuth telluride-based powders is a challenge. An ALD reactor that fluidizes or agitates the powders can be adapted for this purpose. In this study, two types of ALD reactors, a gas fluidization reactor and a rotary reactor, were used to coat selenium-doped bismuth telluride powders with ZnO. Uniform and conformal ZnO layers were successfully grown using both the ALD reactors. However, the crystalline structure, particle size distribution, and chemical bonding states of ZnO were affected by reactor type. Pelletization of the ALD-coated powders was performed by spark plasma sintering at a high temperature (500 °C) and pressure (60 MPa). The morphologies of the powders did not change with palletization; however, differences in the chemical states of the ZnO layers on the BTS powders were observed. It was observed that the remnant water molecules and mobile ion species might compensate for the carrier mobility in pellets made of ALD-coated powders.     

Elemental mercury vapor capture by powdered activated carbon in a fluidized bed reactor

A bubbling fluidized bed of inert material was used to increase the activated carbon residence time in the reaction zone and to improve its performance for mercury vapor capture. Elemental mercury capture experiments were conducted at 100 °C in a purposely designed 65 mm ID lab-scale pyrex reactor, that could be operated both in the fluidized bed and in the entrained bed configurations. Commercial powdered activated carbon was pneumatically injected in the reactor and mercury concentration at the outlet was monitored continuously. Experiments were carried out at different inert particle sizes, bed masses, fluidization velocities and carbon feed rates. Experimental results showed that the presence of a bubbling fluidized bed led to an increase of the mercury capture efficiency and, in turn, of the activated carbon utilization. This was explained by the enhanced activated carbon loading and gas-solid contact time that establishes in the reaction zone, because of the large surface area available for activated carbon adhesion/deposition in the fluidized bed. Transient mercury concentration profiles at the bed outlet during the runs were used to discriminate between the controlling phenomena in the process. Experimental data have been analyzed in the light of a phenomenological framework that takes into account the presence of both free and adhered carbon in the reactor as well as mercury saturation of the adsorbent.