Catalyst design by CFD for heat transfer and reaction in steam reforming

A comparative study was made of the influence on heat transfer performance in the near-wall region, of internal voids in cylindrical particles, in a steam reforming packed bed reactor tube. Computational fluid dynamics (CFD) was used to obtain detailed flow and temperature fields in a representative wall segment of the tube. Simulations in which inert packing was heated up showed that particles with no internal voids appeared to perform better than particles with internal voids, in the bed interior. Near the wall, all particles behaved similarly. When heat sinks were included in the particles to represent the thermal effects of chemical reaction, the heat transfer performance of a packing of full cylinders was shown to change markedly, both qualitatively and quantitatively.     

A mathematical simulation of radiant heat transfer in a cylindrical furnace

The radiative heat transfer in a cylindrical furnace was investigated both experimentally and theoretically. The flow pattern within the combustion chamber was measured and found to differ from that of an identical cold model for which extensive theoretical and experimental work had been previously carried out. The Monte Carlo Method was used to solve for the radiative transfer part of the non-linear integro-differential equations describing the combustion and heat transfer in a cylindrical furnace. The radiative heat flux distribution obtained from the simulation agreed well with data obtained from a cylindrical test furnace.     

Simulation of natural gas steam reforming furnace

A mathematical model for natural gas reformer is established to draw up homogeneous phase one-dimensional reaction kinetics equation in the reforming tubes, and compute the tube external radiant heat transfer with zone method. Simulation result is compared with the operating data carried on Selas reformer used in Brown and Root Braun 1000 t NH₃/day production system in Urumqi Second Ammonia Plant, and they match well. This model has laid the foundation for the design variable optimization research, for example, the relations among specific heat transfer area of furnace tube, tube outlet temperature, tube pressure drop and maximum tube-wall temperature, as well as the effect of tube pitch, furnace chamber width, burner arrangement, furnace wall blackness, production load, water carbon ratio and fuel distribution on operation behaviors.     

Process simulation of natural gas steam reforming: Fuel distribution optimisation in the furnace

This paper describes a two-step method to simulate the natural gas steam reforming for hydrogen production. The first step is to calculate reforming tube length and fuel distribution with equilibrium approach associated with heat transfer. The second step is to calculate and validate reforming performance with kinetic model. A short-cut simulation of hydrogen plant has also been performed to calculate inputs for the reformer model, such as total flow rate and composition of mixed fuel burning in the furnace chamber. Heat transfer, especially radiative heat transfer, is the key role in the steam reforming technology, due to the high heat fluxes involved. For this reason, energy modelling of the furnace chamber has been performed. The simulation evaluates the most important design variables, as tubes height, maximum tube-wall temperature, and tube pressure drop. The heat flux profile can be selected to have suitable metal temperatures to lengthen the reformer tube life. The model calculates the design parameters for reforming tube and fuel distribution among burners.     

一种新型多晶硅还原炉流动与传热的数值模拟

在传统多晶硅还原炉结构基础上,提出了一种内部流场为平推式流动的新型多晶硅还原炉,并采用计算流体力学方法研究了该还原炉内的速度场和温度场。流场模拟结果表明,新型多晶硅还原炉内混合气的流动基本上实现了平推式流动;温度场模拟结果发现,通过改变操作参数,采用平推式流动可实现炉内温度场的控制,解决了传统还原炉局部温度过高的问题,可避免硅粉的产生,长期保持还原炉内壁面的抛光效果,降低还原炉辐射电耗;计算结果表明,在相同的条件下,采用新型多晶硅还原炉的还原电耗较传统还原炉可降低8.5%。     

蓄热式换热器传热过程的数值模拟

以某钢铁公司炼铁厂的热风炉为例 ,根据热风炉的实际运行状况对蓄热式换热器内的流动与换热过程进行合理的简化。基于热传导方程、气体流动方程和气体的热平衡方程 ,利用有限差分方法 ,对蓄热体内的导热及其与气体间的换热情况进行数值求解 ,得到蓄热式换热器在开炉、正常的蓄热体加热及冷却三个工作状况下的气体温度与蓄热体温度随时间的变化规律 ,以及气体温度与蓄热体的温度沿蓄热体高度的分布规律。计算结果表明 ,对蓄热式换热器流动换热模型所作的简化是合理的 ,数值模拟的结果也是基本符合实际运行情况的     

甲醇水蒸汽重整制氢反应的热力学分析

针对甲醇水蒸汽重整制氢反应体系,通过理论计算研究了化学平衡常数随温度的变化规律,指出该反应适宜的反应温度。选取自行开发的CuZnZrAlO催化剂作为研究对象,比较了反应体系中理论平衡组成和实际组成之间的差别,研究了体系中两个独立反应——甲醇分解和水蒸汽变换的反应进度受温度影响的敏感度。通过比较实际反应性能和理论平衡极限的差别,为CuZnZrAlO催化剂的进一步改进提供了研究方向。     

Effect of particle shape on fluid flow and heat transfer for methane steam reforming reactions in a packed bed

Numerical simulations of a cylindrical packed bed with tube to particle diameter ratio of 1.4, containing 10 particles, were performed to understand the effect of particle shape on pressure drop, heat transfer and reaction performance. Six particle shapes namely, cylinder as the reference, trilobe and daisy having external shaping, hollow cylinder, cylcut, and 7‐hole cylinder including internal voids were chosen. Methane steam reforming reactions were considered for the heat transfer and reaction performance evaluation. The present study showed that the external shaping of particles offered lower pressure drop, but lower values of effectiveness factor indicating strong diffusion limitations. The internally shaped particles offered increased surface area, led to higher effectiveness factor and allowed to overcome the diffusion limitations. The effective heat transfer and effectiveness factor of the trilobe‐shaped particle per unit pressure drop was found to be the best among the particle shapes considered in the present work. © 2016 American Institute of Chemical Engineers AIChE J, 63: 366–377, 2017     

一种新型裂解炉炉管强化传热数值模拟

利用计算流体动力学(computational fluid dynamic,CFD)方法对含新型内插件强化传热辐射炉管(fortified induced turbulence,FIT)进行了流体流动与传热特性的研究,采用RNG双方程模型求解了动量方程和能量方程,给出了FIT炉管内的流体流动和传热特性,包括速度场、湍动强度和温度场的分布;计算了FIT炉管的强化传热因子和压降。研究结果表明,FIT炉管内插件迫使流体流动由活塞流转变为旋转流,增强了流动湍流程度,符合流动-能量场协同理论,同时流体边界层由于FIT炉管的特殊结构而减薄。FIT炉管具有增强辐射传热、减薄边界层、增加比表面积和旋流增强等强化传热特性。相比于普通当量圆炉管,FIT强化传热炉管的整体传热能力提高了20%左右,证明该新型炉管强化传热效果显著,可以在工程实际中应用。     

应用1.0 MPa蒸汽作为热媒炉雾化蒸汽的试验

针对辽阳石化公司PET热媒炉在运行中使用的燃料油相比原设计工况条件下黏度减小的现状,从节能降耗角度出发将原设计使用的1.6 MPa蒸汽调整为1.0 MPa蒸汽,并对其运行状况进行考察。试验结果表明,在选择合适的时间段内,保证蒸汽含水率低的情况下,用1.0 MPa蒸汽替代1.6 MPa雾化蒸汽能够保证热媒炉稳定运行。     

熔渣颗粒空冷相变换热的三维数值模拟

利用VOF方法结合凝固和熔化模型对熔渣颗粒在空气流中的冷却相变过程进行了三维数值模拟,讨论了熔渣颗粒直径和空气速度对冷却凝固过程演变的影响。结果表明：空冷方法能够实现熔渣颗粒表面的快速凝固成型,但同时也造成了颗粒内部的非均匀凝固。熔渣直径越小,完全凝固时间越短;空气流速越大时, 其表面换热越强, 完全冷却时间越短。颗粒初温为1673.15 K、直径为0.5~2 mm,风速为1~5 m·s^-1条件下熔渣颗粒在2 s内释放出全部凝固热,后续空气最高温度能达到900 K以上。     

非热平衡多孔介质内反应与传热传质耦合过程

采用局部热不平衡假设,对发生强吸热化学反应的多孔介质体系建立了反应与传热、传质耦合问题的数学模型,采用Ergun-Forchheimer-Brinkman方程描述多孔介质中的流体流动.运用交替方向隐式(ADI)方法对模型离散求解,并采用文献中的实验数据对模型进行验证.计算了不同条件下颗粒物料层内气体和固体骨架的温度场、产物气体浓度场以及固体转化率分布,以得到多孔介质体系内固有化学反应时的传热、传质规律.结果表明,不能忽略固体骨架与流体间的温度差.入口渗流速度、入口气体温度以及固体颗粒尺寸是影响系统反应特性的重要参数.研究结果对具有强吸热反应的固定床反应器的设计和运行具有一定的参考作用.     

微型流化床中焦油热裂解和水蒸气重整的反应特性及动力学对比

采用微型流化床反应分析仪(MFBRA)考察了不同温度(T,750~950℃)和水蒸气分压(SP,10%~30%)下生物质焦油水蒸气重整过程中的气体生成、气体产物中总碳转化和焦油转化等反应特性,求算反应动力学,并与焦油热裂解特性进行比较。在热裂解过程中,随温度增加,各气体(H₂、CH₄、CO、CO₂)产率和气体产物中的总碳转化率增加,反应时间缩短。而在焦油水蒸气重整过程中,等温下的反应时间明显延长,且H₂、CH₄、CO产率和气体产物中的总碳转化率显著提升,而CO₂产率在850℃时有最大值。在焦油水蒸气重整过程中,不仅有焦油裂解,还有裂解产物与水蒸气的反应,促进碳转化。在950℃、SP=30%条件下,气体产物中的总碳转化率达到92.34%。水蒸气作用下,气体组分的产率和气体产物中的总碳转化率增加,而等温条件下的反应速率下降。水蒸气分压对各气体组分的影响具有差异性。随分压增加,CO、CH₄的生成速率和气体产物中的总碳转化的反应速率增加;H₂生成速率逐渐下降,速率稳定段扩大;CO₂生成速率在850℃时有最大值。采用均相模型求取焦油水蒸气重整反应过程中的活化能,气体产物的生成活化能(H₂、CO、CO₂和CH₄)、气体产物中的总碳转化及焦油转化的活化能明显偏低,分别为90.10、42.01、58.56、64.92、61.44和63.26 kJ/mol,对应数值明显小于焦油热裂解,说明水蒸气对焦油重整反应的促进作用。最后,将焦油热裂解动力学数据与文献数据对比,验证了MFBRA对焦油水蒸气重整反应测试的可行性和分析结果的准确性。     

甲醇蒸汽重整制氢反应动力学研究进展

甲醇蒸汽重整制氢技术对于解决汽车、船舶等交通工具上燃料电池的氢源问题具有重要意义,近年来已成为碳氢燃料重整制氢的研究热点。本文首先综述了甲醇蒸汽重整制氢的5种反应机理,该方面的研究仍处于定性和推理阶段,尚未达成统一的结论。然后分析了甲醇蒸汽重整反应动力学的研究进展,发现大多研究是基于Cu系催化剂提出,反应温度集中在160～350℃,反应压力多为1atm,研究表明反应物水醇比最优值为1.3～1.4。最后,整理了研究中所提出的动力学模型,指出相较于单速率和三速率模型,双速率模型可反映产物中CO的含量及其对反应速率的影响,且模型相对简单,动力学方程的求解过程也相对容易,但其适用性还有待进一步验证。本文可为甲醇蒸汽重整制氢系统的设计与优化提供理论依据。     

催化剂颗粒形状对甲烷水蒸气重整反应的影响及工业反应器模拟

甲烷水蒸气重整工艺是现阶段最主要的工业制氢技术,催化剂颗粒形状和反应器操作条件是影响重整反应器性能和产物组成的重要因素。首先从颗粒尺度研究催化剂形状对甲烷水蒸气重整反应的影响,在不同的反应温度和压力下,计算并比较了球形、柱形和环形催化剂的效率因子,其大小顺序为:柱形 < 球形 < 环形。其次,将反应器床层的质量、热量和动量传递与环形催化剂颗粒的扩散-反应方程相结合,建立了用于描述甲烷水蒸气重整工业反应器的一维轴向数学模型。计算并分析了反应器进口温度和压力对反应器床层的温度和压力分布、催化剂效率因子以及甲烷转化率和各组分浓度分布的影响,确定了适宜的工业反应器进口温度和压力,分别为773 K和3 MPa。     

Methane steam reforming in a Pd-Ru membrane reactor

Methane steam reforming has been carried out in a Pd-Ru membrane reactor at 500–600 ‡C. The membrane reactor consisted of a Pd-6%Ru tube of 100 mm wall thickness and commercial catalysts packed outside of the membrane. The methane conversion was significantly enhanced in the membrane reactor in which reaction equilibrium was shifted by selective permeation of hydrogen through the membrane. The methane conversion at 500 ‡C was improved as high as 80% in the membrane reactor, while equilibrium conversion in a fixed-bed reactor was 57%. The effect of gas flow rate and temperature on the performance of the membrane reactor was investigated and the results were compared with the simulated result from the model. The model prediction is in good agreement with the experimental result. In order to apply the membrane in practice, however, the thickness of the membrane has to be reduced. Therefore, the effect of membrane thickness on performance of the membrane reactor was estimated using the model.     

硅藻土基调湿材料中热湿耦合传递

建立了硅藻土基调湿材料内部热湿耦合迁移一维数学模型,模拟了不同孔隙率、不同环境温度和相对湿度下硅藻土基调湿材料中的热湿耦合迁移过程,结合硅藻土基调湿材料调湿性能实验测试结果以及硅藻土基调湿材料表面的显微图像分析,研究结果表明：随着孔隙率的减小,硅藻土基调湿材料的吸、放湿量均增大;环境温度对硅藻土基调湿材料热湿耦合迁移过程影响不显著,不同的环境温度（最大相差20℃）对硅藻土基调湿材料吸、放湿量的影响均在10%左右;硅藻土基调湿材料的孔径尺寸越小、小孔径孔隙数量越多,其调湿性能越好;硅藻土基调湿材料调湿性能的实测数据、模拟结果以及图像表征吻合良好,从而验证了理论模型的合理性。     

Oxygen transfer and catalytic properties of nickel iron oxides for steam reforming of methane

Nickel iron oxide (NiFe₂O₄) has been tested as a combined catalyst precursor and oxygen transfer material for improved conversion of methane into syngas. Thermogravimetric measurements with simultaneous gas analysis have demonstrated the superior behavior of nickel iron oxide compared to iron oxide. The enhanced catalytic activity is attributed to the generation of fresh nickel surfaces in the course of the reduction of the metal oxide. This allows for a periodic in situ generation of fresh, catalytically active nickel.     

Curing and heat transfer in polyurethane reaction molding

Temperature measurements were made on the adiabatic polymerization of three urethane systems; two casting formulations, one thermoplastic and the other thermosetting, and a commercial reaction injection molding (RIM) formulation with a 10 second gel time. The data were found to fit a simple nth order overall kinetic expression. These kinetic and heat of reaction results were used to model heat transfer in a 3.8 cm diameter cylinder with an isothermal wall. Experimental temperature profiles for the two casting urethanes were in good agreement with predictions. The kinetic data on the RIM material was used to model temperature profiles1 in 3 and 6 mm thick plaque molds. Experimental measurements of temperature near the mold center agreed with the model. Temperatures measured near the wall were higher due to failure of the isothermal wall assumption.     

Preliminary design and simulation of a microstructured reactor for production of synthesis gas by steam methane reforming

The present study considers the potentials of the well-known production of syngas by steam methane reforming (SMR), by operation within microstructured reactors. The model of a microchannel reactor is developed, including very fast kinetic reaction rates on the coated catalytic walls of the reactor module. By varying the characteristic dimensions of the channels, and considering technical constraints on the design and operating conditions, the results demonstrate that the SMR reactor can be drastically miniaturized while maintaining its productivity without any additional pressure drop. Furthermore, by reducing the channel characteristic dimensions, it is possible to suppress heat and mass-transfer limitations enabling SMR reactor operation at thermodynamic equilibrium. A fast method for preliminary design of microstructured heat-exchanger reactors is developed, that enables to identify the optimal channels number and heat power needed to reach process specifications.