工业级错流列管式固定床反应器的CFD模拟

工业级大型列管式固定床反应器壳程温度场与流场的均匀程度与反应的转化率及选择性密切相关。通过添加阻力源项和分散热源项,对工业级全尺寸错流列管式固定床壳程流场及温度场进行了CFD模拟研究,并进一步考察了折流板窗口区大小及其位置对壳程压降与温度分布的影响。结果表明,模拟得到壳程压降与由经验公式计算得到的压降较为接近,且壳程温度分布与工业实际数据吻合;增大窗口区面积,壳程压降呈现指数下降,同时高温差区（径向温差大于2 K）的范围与径向温差变大;随着第1块折流板位置降低,高温差区范围及径向温差均减小,但压降并不呈现规律性变化。模拟方法可用于工业级大型列管式固定床反应器的优化及设计。     

双催化层固定床甲烷化反应器CFD模拟

温度分布直接影响着固定床甲烷化反应器的甲烷产量和设备安全性。以年产12.75亿立方煤制天然气绝热甲烷化反应器为研究对象,在建立真实设备三维模型的基础上,利用ANSYS-CFX有限元数值模拟的方法,建立多孔介质内化学反应、热交换与质量传递的气-固两相反应器模型,获得了双段固定床甲烷化反应器内部温度、压力、速度场的分布规律及甲烷产率分布。对不同床层结构对应的特征场分布进行了探索,分析了床层结构对各特征场分布的影响,确定了床层结构优化方案,MCR催化剂床层出口处支撑延长的结构更有利于温度场沿反应器径向的均匀分布和甲烷质量分数的提高。对反应器入口温度、空速、压力对特征参数分布的影响进行了研究,提出了针对本工艺的允许入口参数波动范围。     

Effect of particle shape on methanol partial oxidation in a fixed bed using CFD reactor modeling

Particle shape is one of the most important parameters in the design and optimization of fixed-bed processes. To address the impact of particle shape on methanol partial oxidation to formaldehyde over molybdate catalyst, packings of spheres, cylinders, rings, and trilobes are numerically generated. The generated packings are used to carry out resolved particle Computational Fluid Dynamics (CFD) simulations under industrial conditions. Pressure drop, voidage and velocity profiles, radial heat transfer, and local and overall conversion and selectivity results are presented. Despite their lower particle surface area, lower particle effectiveness and more uneven flow distribution than trilobes, and lower overall heat transfer coefficient than cylinders, rings had the best conversion and selectivity due to their balance between the factors. Three longer tubes of rings, rings and cylinders, and rings and trilobes are simulated and show a small gain in selectivity for the rings and trilobes.     

煤层气水合物定容生成实验研究

为了有效利用与回收直接排放的大量抽放瓦斯,提出了利用水合物技术处理与储运的新方法,根据气体成分确立了水合物生成的温度与压力条件,通过对气体进行初始压力为9.5 MPa的定容法实验,研究了含表面活性剂下水合物生成过程中温度-压力与CH4转化率的变化规律。实验结果表明,水合反应的进行应保持一定的反应驱动力,根据不同温度下反应驱动力进而确定最佳反应条件,同时反应过程中CH4能被有效提取,但要进行高效生产,应进行多级水合分离技术以提高产率。     

Oxygen selective ceramic hollow fiber membranes for partial oxidation of methane

A BaCo_xFe_yZr_zO_3?δ (BCFZ) perovskite hollow fiber membrane was used to construct reactors for the partial oxidation of methane (POM) to syngas. The performance of the BCFZ fibers in the POM was studied (i) without any catalyst, (ii) with catalyst‐coated fibers, and (iii) with catalyst packed around the fibers. In addition to the performance in the POM, the stability of the BCFZ hollow fiber membranes was investigated for the different catalyst arrangements. Best stability of the BCFZ hollow fiber membrane reactor in the POM could be obtained if the reforming catalyst is placed behind the oxygen permeation zone. It was found that a direct contact of the catalyst and the fiber must be avoided which could be achieved by coating the fiber with a gold film. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

甲烷部分氧化制乙炔过程研究

The partial oxidation of hydrocarbons is an important technical route to produce acetylene for chemical industry.The partial oxidation reactor is the key to high acetylene yields.This work is an experimental and numerical study on the use of a methane flame to produce acetylene.A lab scale partial oxidation reactor was used to produce ultra fuel-rich premixed jet flames.The axial temperature and species concentration profiles were measured for different equivalence ratios and preheating temperatures,and these were compared to numerical results from Computational Fluid Dynamics(CFD)simulations that used the Reynolds Averaged Navier-Stokes Probability Density Function(RANS-PDF)approach coupled with detailed chemical mechanisms.The Leeds 1.5,GRI 3.0 and San Diego mechanisms were used to investigate the effect of the detailed chemical mechanisms.The effects of equivalence ratio and preheating temperature on acetylene production were experimentally and numerically studied.The experimental validations indicated that the present numerical simulation provided reliable prediction on the partial oxidation of methane.Using this simulation method the optimal equivalence ratio for acetylene production was determined to be 3.6.Increasing preheating temperature improved acetylene production and shortened greatly the ignition delay time.So the increase of preheating temperature had to be limited to avoid uncontrolled ignition in the mixing chamber and the pyrolysis of methane in the preheater.     

CFD simulations of quenching process for partial oxidation of methane:Comparison of jet-in-cross-flow and impinging flow configurations

A new quenching process using the cold pyrolysis gas has been proposed for the partial oxidation (POX) of methane to recover the heat.The mixing of hot product gas and cold pyrolysis gas in milliseconds is critical to this new approach.Two most widely-used rapid mixing configurations,i.e.the jet-in-cross-flow (JICF) and impinging flow configurations,are compared in terms of mixing and quenching performances using computational fluid dynamics (CFD) coupled with detailed reaction mechanism Leeds 1.5.The mixedness,residence time distribution,temperature decreasing rate and loss ratio of acetylene during the quenching are systematically studied.The results show that the impinging flow has a more uniform mixing and narrower residence time distribution than the JICF.However,the temperature decreasing rate of the mainstream is faster in the JICF than in the impinging flow.The loss ratio of acetylene in the quenching process is 2.89％ for the JICF and 1.45％ for the impinging flow,showing that the impinging flow configuration is better and feasible for the quenching of POX of methane.     

Methane partial oxidation to methanol-solid initiated homogeneous methane oxidation

The initiation temperature of methane partial oxidation was markedly lowered by platinum wire placed upstream of a high pressure reactor. Added hydrogen in the reactant gas promoted the methanol selectivity. The radicals formed on the platinum surface were desorbed from it and initiated the reaction.     

Axial variation of the oxidation state of Pt-Rh/Al2O3 during partial methane oxidation in a fixed-bed reactor: An in situ X-ray absorption spectroscopy study

Probing the structure of materials in situ is of central importance in heterogeneous catalysis. Mostly, this is done in an integral manner, that is without spatial resolution. However, at high conversion in a catalyst bed prominent concentration and/or temperature profiles may exist which can result in significant spatial variation of the catalyst structure. In the present study, X-ray absorption spectroscopy combined with on-line mass spectrometry was used to monitor the structural changes of a Pt-Rh/Al₂O₃ catalyst in a fixed-bed reactor during partial oxidation of methane. The reaction ignited at 310 °C and integral X-ray absorption spectroscopy showed that the Rh-Pt-particles were reduced at the same time. However, monitoring with a beam of 1 mm × 0.6 mm size along the axial position of the catalyst bed uncovered that Rh and Pt were still in oxidized state in the entrance region, whereas they were in reduced state in the zone at the end of the catalyst bed. The gradual transition from the reduced to the oxidized state was found to shift towards the bed entrance if the temperature was slightly increased.An erratum to this article can be found at .     

Catalytic partial oxidation of methane in a novel heat-integrated wall reactor

A novel reactor has been developed and applied in the reaction of partial oxidation of methane to synthesis gas. The reactor consists of a ceramic tube in the inner and outer surface of which a metal catalyst film is deposited. The CH₄/O₂ feed enters into the tube and a large fraction of the heat generated on the wall by methane combustion is transported across the tube wall towards the outer catalyst film, where the endothermic reforming reactions take place. In this way, the temperature in the combustion zone is controlled and hot spots are significantly reduced in magnitude. Initial results presented in this work demonstrate the feasibility of the concept. This revised version was published online in July 2006 with corrections to the Cover Date.     

CFD analysis of low temperature water gas shift reactor

In the design of water gas shift reactors, the performance of catalysts is not known a priori and hence having a general kinetic expression will be of much help. Computational Fluid Dynamic study was carried out to investigate the performance of a packed bed reactor for different feed compositions using five commonly used types of macro kinetic models. User Defined Functions were developed for the reaction rate to predict the CO conversion in the reactor. The effects of temperature and time factor on CO conversion were studied. The Langmuir-Hinshelwood model gave the best prediction for H₂ rich mixtures. The Temkin model was better for higher CO concentrations, whereas the other models gave large deviations for the fixed bed reactor.     

耦合传质的羰基化固定床反应器传热模拟分析

固定床反应器中进行强放热反应时, 反应器的热点温度对操作参数变化敏感,容易引起飞温,导致转化率下降,影响催化剂寿命。为强化羰基化固定床反应器内热质传递与化学反应的协同性,建立考虑颗粒内扩散影响的羰基化固定床反应器拟均相一维传热模型,考察操作参数对床层热点温度、反应转化率、床层温升的影响。不仅体现传热传质和反应的协同作用,而且影响关系明晰、求解方便。为保证反应转化率,本实验条件下确定催化剂颗粒直径小于等于1.5 mm。反应器入口温度/冷却剂油温既要满足床层热稳定性需求,又要使反应转化率和床层温升都在合理范围内。模拟结果表明在床层入口温度升高的同时,可通过降低冷却剂油温获得良好的反应转化率和较小的床层温升。在此基础上,考察入口环氧乙烷浓度对反应转化率和床层温升的影响。本研究可为固定床反应器满足转化率要求、床层合理温升而选择催化剂颗粒直径、床层入口温度、冷却剂油温和床层入口浓度等操作参数提供计算依据。     

Catalytic partial oxidation of methane to syngas in a fixed-bed reactor with an O2-distributor: The axial temperature profile and species profile study

Catalytic partial oxidation of methane (CPOM) to syngas has been investigated in a fixed-bed reactor with an O₂-distributor (FR-OD). The axial temperature profile and species profile along the Ni or Rh-based catalyst bed have been measured at different conditions. As the O₂ was distributed radially into the catalyst bed through several rows of holes arranged at the special zone of the OD, a microenvironment maintaining a low O₂/CH₄ ratio (0.10–0.22) was provided in the catalyst bed. The hotspot phenomena appeared at the entrance of the catalyst bed have been effectively controlled. A more uniform temperature profile along the catalyst bed has been given, which is beneficial to the stability of catalyst and the safety of reactor operation.     

Rh负载的整体型催化剂甲烷催化部分氧化过程

采用负载Rh的泡沫独石整体型催化剂研究了甲烷催化部分氧化过程,考察了外界温度、空速和甲烷与氧气进料比例对反应转化率和选择性的影响,并对过程控制条件和调控参数进行了分析。研究结果表明该过程为毫秒级超短接触过程,反应可以在自热条件下进行,高空速条件下（8×10⁵ h^-1）,甲烷与氧气进料比（体积比）为1.8,甲烷转过率超过90%,CO选择性接近95%,H₂选择性超过90%。外界加热对过程有利,可获得更高的转化率和选择性。     

甲烷常压非催化部分氧化热模实验研究

氧气/甲烷摩尔比、操作负荷以及二氧化碳添加的研究对天然气非催化部分氧化转化炉运行优化和调节合成气氢气/一氧化碳摩尔比非常重要。文中搭建了天然气非催化部分氧化热模实验平台,考察了上述因素对出口合成气组成的影响。在研究范围内得出以下结论:氧气/甲烷摩尔比从0.85增加到1.10,出口甲烷摩尔分数随之降低,有效合成气(一氧化碳+氢气)摩尔分数先增大后减小,在氧气/甲烷摩尔比为0.95时达到最大值87.75%;由于壁面热损失和停留时间的影响,提升操作负荷有利于提高有效合成气摩尔分数,但会导致甲烷转化率下降;添加的二氧化碳参加了逆水蒸气变换反应及甲烷二氧化碳重整反应,使合成气中一氧化碳摩尔分数随二氧化碳/甲烷摩尔比的增加而增加,氢气的变化趋势则与之相反。     

Improving selectivity during methane partial oxidation by use of a membrane reactor

A reactant-swept catalytic membrane reactor for partial oxidation of methane to formaldehyde has been modeled. Kinetic parameters were taken from the literature for a V₂O₅/Sio₂ methane partial oxidation catalyst, and membrane parameters characteristic of commercially available materials were used. The models show that the selectivity for formaldehyde can be significantly improved by using a membrane reactor.     

Catalytic partial oxidation of methane to synthesis gas in a ceramic membrane reactor

Methane has been selectively converted to synthesis gas using a two-zone fixed bed of a Ni/Al₂O₃ catalyst inside a modified ceramic membrane. The first zone of the reactor was surrounded by an impervious wall, and therefore behaved as a conventional fixed bed reactor. In the second zone, some of the reaction products could preferentially diffuse out of the reactor, which yielded higher than equilibrium methane conversions. The influence of the different operating conditions has been studied, and the performance of the membrane reactor has been compared to that of a fixed bed reactor. The membrane reactor has also been used at pressures above atmospheric (2 bar), with good conversions and selectivities.     

聚合釜传热性能的实验研究及数值模拟

基于CFD模拟与传热实验相结合的方法对5 L夹套聚合釜的传热性能进行研究。建立聚合釜的液固耦合稳态传热模型,获得釜内流体、夹套内流体及金属固体域内温度分布。开展传热实验对模拟结果进行验证,各对比点温度的最大相对误差在1%~5%范围内。通过模拟获得釜内外壁面传热系数及总传热系数,并关联出釜侧及夹套侧 Nu的经验式。结果表明：釜内流体温度分布方差始终在0.002以下,固体域内和传热边界层温度梯度较大,传热边界层厚度约3.8 mm;实验范围内,入口温度和反应放热量对釜内温度的影响显著,入口流速次之,搅拌转速影响最弱;夹套侧传热系数远小于釜侧传热系数,提高夹套侧传热系数是提升传热性能的关键;实验用聚合釜外表面散热量与内外温差呈正比,比例系数约为3.031 W·K ^-1。     

Analysis of catalytic partial oxidation of methane on rhodium-coated foam monolith using CFD with detailed chemistry

CFD simulation with detailed chemistry was conducted to understand the catalytic partial oxidation of methane (CPOM) on rhodium-coated foam monolith. For the underlying process occurred extremely fast with large gradients of temperature and species concentrations at the inlet, special attention must be paid to the appropriate treatment on computational geometry and corresponding boundary conditions for the simulation. Discussions were made carefully on this proposed issue in geometry modeling that the reliable predictions can be authentically obtained by adopting the same geometry as the experiments from the viewpoint of physics in order to fully consider the heat conduction/diffusion at the reactor inlet. The right model system was sufficiently validated by both the conceptual analysis and the experimental results. The reactor performance of CPOM process was thereafter studied by numerically revealing the effects of wall heat conduction, the channel diameter and the catalytic surface area on the profiles of temperature and species concentrations. The results showed that the maximum wall temperature, which was crucial for the catalyst stability, could be significantly reduced by increasing the thermal conductivity of the wall, and/or the channel diameter, and/or the catalytic surface area, but accompanied with a slight drop of the methane conversion. This deficiency can be retrieved by decreasing the atom feed ratio of C/O and/or elongating the catalytic bed. These results pointed out the necessity of facilitating the foam material, the channel diameter and the catalytic surface area with the operating conditions in order to achieve the best performance of the CPOM process in the millisecond reactor.