微通道尺寸对甲烷蒸汽重整性能的影响

联合使用可计算表面反应的化学反应动力学软件CHEMKIN4.0和CFD软件,对平板微反应器中Ni催化剂涂层上的甲烷蒸汽重整制合成气进行了数值计算,并结合表面活性组分的分布分析了微通道长度、高度对蒸汽重整性能的影响.计算结果表明:甲烷蒸汽重整受CO(S)的解吸速率控制;反应通道高度减小,从而减少反应物和产物在通道中扩散所需要的时间并增大反应控制组分CO(S)的表面覆盖率,使得甲烷的转化率和产物中的氢含量提高;反应通道长度增大,反应物与催化剂的接触时间延长,甲烷的转化率和氢含量提高.这对进行微通道甲烷蒸汽重整的实验研究以及平板微通道反应器的设计和优化提供了理论依据.     

固体氧化物燃料电池与燃气轮机混合发电的发展及甲烷蒸汽重整的研究

燃料电池与燃气轮机混合发电系统有着很高的能量利用效率,是能量转换的重要研究方向。而固体氧化物燃料电池的蒸汽重整技术为该联合提供了重要的技术支持。本文设计了固体氧化物燃料电池的结构,并进行甲烷蒸汽重整的模拟计算,计算结果显示燃料电池排气温度达到1380K左右时,有很高的能量利用价值。     

重整条件对SOFC电池堆性能影响的实验研究

以天然气为燃料,建立了外部重整固体氧化物燃料电池(SOFC)系统的实验平台,在不同重整工艺参数条件下,对电池堆的性能进行了测试,得到了电池堆性能参数的变化趋势,分析了水碳物质的量比(即水碳比)、重整温度、重整方式以及天然气体积流量对SOFC电池堆性能的影响.结果表明:在不同的电流密度下,采用水蒸气重整方式电池堆的输出功率高于自热重整方式电池堆的输出功率;当电池堆工作温度设定恒值为1 023K时,随着水碳比的增大,电池堆的输出功率逐渐提高,随着天然气体积流量的增加,电池堆的输出功率显著提高.     

固体氧化物燃料电池直接内重整的模型研究进展

固体氧化物燃料电池(SOFCs)是一种通过电化学氧化反应直接将化学能高效率地转化为电能的装置,在大规模发电、联产以及一体化燃料升级等可再生能源系统领域具有广阔的市场前景.为进一步拓宽SOFCs的应用场景,降低运行成本,直接内重整(DIR)技术可将CH4等烷烃类物质在阳极催化生成H2,减少了燃料预处理要求且提高了转化效率,是目前SOFCs研究领域的热点之一.为了优化该技术的系统设计和操作条件,模型模拟的研究可显著减少实验工作量,并为其提供理论支撑和指导性建议.通过DIR-SOFC系统的模型模拟,结合场分布、动力学参数等,可以量化评估系统内的反应,从而了解其物理、化学过程的复杂性.本文总结了DIR-SOFC建模工作的现状,介绍了体积平均模型和针对微观结构的模型;重点讨论多尺度数学模型,对现有研究中的反应动力学过程描述、\"能量-质量-动量\"平衡方程、\"1D-2D-3D\"DIR-SOFC单元描述等进行了综述,能更好地评估变量对DIR的影响;对DIR-SOFC模型中不同液体燃料的重整反应及相关的反应动力学参数进行总结;指出现有模型的不足,并对DIR-SOFC系统模型的未来发展进行展望,使模型更加精准.     

甲烷混合燃料气内重整反应对平板式固体氧化物燃料电池性能影响

为研究经过预重整的含甲烷混合燃料气中甲烷浓度及内部重整对平板式固体氧化物燃料电池电化学性能和热机械性能的影响,建立甲烷内重整平板式固体氧化物燃料电池模型,并对多孔材料的弹性模量及泊松比进行修正,对比3种不同甲烷浓度条件下电池的综合性能。结果表明：在电化学性能方面,随着混合燃料气中甲烷浓度的增大,电池电流密度和功率密度逐渐增大,流道中甲烷的摩尔浓度沿燃料流动方向逐渐减小,氢气浓度沿流动方向呈先增大后减小的趋势,氢气的最大浓度逐渐远离燃料入口;热机械性能方面,随着混合燃料气中甲烷浓度的增大,位于金属连接体上的电池最大第一主应力和位于燃料出口的电池最大温度逐渐降低。适当提高混合燃料气中甲烷的浓度有利于平板式固体氧化物燃料电池的综合性能优化。     

天然气水蒸气重整与SOFC耦合应用

固体氧化物燃料电池（SOFC）系统具有高能源效率和使用可再生燃料的可能性,将在未来的可持续能源系统中发挥重要作用。过去几年燃料电池的发展很快,但在成本、稳定性和市场份额方面,该技术仍处于早期发展阶段。在以天然气为燃料的SOFC系统中,燃料的重整过程和燃料利用水平都可能影响系统运行的稳定性、热量和能量平衡,从而影响系统的使用寿命、输出功率和效率。因此,对燃料重整过程的设计与控制对有效的SOFC电池运行具有重要意义。对天然气在SOFC系统中的重整器配置方式（包括外重整和内重整）、重整参数和重整燃料利用方式进行了详细的综述分析,并对未来天然气SOFC系统的发展进行了展望。     

天然气重整SOFC/MGT混合分布式供能系统性能分析

针对固体氧化物燃料电池(SOFC)与微型燃气轮机(MGT)构成的混合分布式供能系统,首先建立了一种管式SOFC准二维数值模型,优化了辐射计算,提高了热传递模型的准确性;考虑了CO及H2同时作为燃料参加电化学反应,并完善了损失计算模型;最后采用所发展的系统性能预测模型,分别在内部重整和外部重整情况下,预测比较了两种SOFC/MGT混合系统的性能,结果表明外部重整系统在系统输出功率、CO2排放以及热应力分布方面都比内部重整系统具有优势,然而这种轻微的优势是需要额外增加外部重整器的设备投资换取的。     

支撑形式及多孔电极结构参数对SOFC性能的影响

研究不同结构设计条件下，活化极化、欧姆极化、浓差极化对SOFC性能的影响。在分析浓差极化时，综合考虑了普通扩散和Knudsen扩散，使模型更接近实际。采用灵敏度分析方法，分析了5个结构参数对SOFC性能的影响。结果表明，在该文的分析条件下，阳极支撑的设计具有较好的输出特性。     

基于树形分叉结构的微通道甲醇重整制氢

针对甲醇蒸汽的微通道重整催化反应过程,建立了三维稳态多组分传输反应模型,利用数值模拟分析,分别研究了平行矩形微通道和树形分叉微通道网络在Zn_Cr/CeO2/ZrO2催化剂下的反应情况。通过双速率模型考察这两种流道中操作条件对甲醇水蒸汽重整制氢输运规律的影响,发现这两种微通道反应器促进了甲醇转化率和氢气产率的提高,且有助于反应器内温度分布均匀;同时相较矩形平行微通道,树形分叉微通道可以进一步提高甲醇的转化率、减小出口CO的含量,是一种理想的适用于质子交换膜燃料电池的制氢流道。     

间接内重整固体氧化物燃料电池的建模与仿真

建立了一维基于催化涂层重整器的间接内重整固体氧化物燃料电池的动态数学模型.在组分和能量守恒的基础上,考虑了电化学模型,建立了基于分布集总参数技术和模块化思想的间接内重整固体氧化物燃料电池的仿真模型.该模＃型不仅能反映燃料电池的分布参数特性,还可以满足动态仿真的需求.利用该模型分析了某一工况下固体氧化物燃料电池的稳态性能,并进行了动态过程的仿真,结果证明该模型可以反映间接内重整固体氧化物燃料电池的基本性能.     

Two-dimensional dynamic simulation of a direct internal reforming solid oxide fuel cell

This study presents a two-dimensional mathematical model of a direct internal reforming solid oxide fuel cell (DIR-SOFC) stack which is based on the reforming reaction kinetics, electrochemical model and principles of mass and heat transfer. To stimulate the model and investigate the steady and dynamic performances of the DIR-SOFC stack, we employ a computational approach and several cases are used including standard conditions, and step changes in fuel flow rate, air flow rate and stack voltage. The temperature distribution, current density distribution, gas species molar fraction distributions and dynamic simulation for a cross-flow DIR-SOFC are presented and discussed. The results show that the dynamic responses are different at each point in the stack. The temperature gradients as well as the current density gradients are large in the stack, which should be considered when designing a stack. Further, a moderate increase in the fuel flow rate improves the performances of the stack. A decrease in the air flow rate can raise the stack temperature and increase fuel and oxygen utilizations. An increased output voltage reduces the current density and gas utilizations, resulting in a decrease in the temperature.     

A detailed surface reaction model for syngas production from butane over Rhodium catalyst

This paper presents numerical and experimental investigations of syngas production from butane. A surface reaction mechanism is used to model the reaction pathways. The butane reforming simulations and experiments are conducted in two reformers (tubular and radial). Starting from the reaction mechanism for methane conversion over a Rh catalyst, a reaction mechanism for butane conversion over the same catalyst is developed. The surface reaction equations are coupled with the flow equations. Porous resistance, catalyst concentration and reaction rate constants of the introduced reaction pathways are estimated by comparing the results of the model with the experimental data. The model is able to capture the main features of the species profiles along the reactors as well as the selectivity trends for different equivalence ratios. Moreover, the model predicts the fractional coverage of the surface species and therefore provides an insight into the reaction mechanisms on the catalyst surface.     

Nonlinear identification of a DIR-SOFC stack using wavelet networks

Application of wavelet networks for identification of a direct internal reforming solid oxide fuel cell (DIR-SOFC) stack is reported in this paper. The SOFC is a complex system particularly when it is directly fueled with hydrocarbons (natural gas, coal gas, etc.). Most of the traditional models of the SOFC, based on the reforming, electrochemical and thermal modeling, are too complicated. To facilitate controller design and analysis of systems, the wavelet network dynamic model of the DIR-SOFC is constructed, avoiding the consideration of the complex processes in the fuel cells. The input and output data are used for initializing and training the wavelet network by a recursive approach. The Gram–Schmidt algorithm, the Cross-Validation method and immune selection principles are applied to optimization of the network. The simulation is performed and comparisons of characteristics under different operating conditions are given. The results show high static and dynamic accuracy of the identified model. Further, the obtained wavelet network model can be used for developing the model-based controllers of DIR-SOFC.     

High temperature electrolyzer based on solid oxide co-ionic electrolyte: A theoretical model

In the present work a theoretical model of a solid oxide electrolyzer based on an electrolyte having both oxygen ion and proton conductivity is considered. The main parameters of the electrolytic process and an electrolyzer (distribution of gas components, electromotive forces and current densities along the electrolyzer channel, average values of electromotive forces and current densities) were calculated depending on a proton transport number and mode of the reactants’ feeding (co- and counter-flow). The performed analysis demonstrates considerable influence of the mode of feeding on all parameters of the electrolyzer: operation under the counter-flow mode is preferable as regards the specific characteristics and uniformity of their distribution along the electrolyzer. It is shown that the electrolyser's specific characteristics increase with the increase of the proton transport number.     

Influence of current densities in SOFC and PEFC stacks on a SOFC–PEFC combined system

A solid oxide fuel cell (SOFC)–polymer electrolyte fuel cell (PEFC) combined system was investigated by numerical simulation. Here, the effect of the current densities in the SOFC and the PEFC stacks on the system's performance is evaluated under a constant fuel utilization condition. It is shown that the SOFC–PEFC system has an optimal combination of current densities, for which the electrical efficiency is highest. The optimal combination exists because the cell voltage in one stack increases and that of the other stack decreases when the current densities are changed. It is clarified that there is an optimal size of the PEFC stack in the parallel-fuel-feeding-type SOFC–PEFC system from the viewpoint of efficiency, although a larger PEFC stack always leads to higher electrical efficiency in the series-fuel-feeding-type SOFC–PEFC system. The 40 kW-class PEFC stack is suitable for the 110 kW-class SOFC stack in the parallel-fuel-feeding type SOFC–PEFC system.     

Effect of operating conditions and gas flow patterns on the system performances of IIR-SOFC fueled by methanol

Mathematical models of an indirect internal reforming solid oxide fuel cells (IIR-SOFC) fueled by methanol were developed to analyze the thermal coupling of the internal endothermic steam reforming with exothermic electrochemical reactions and predict the system performance. The simulations indicated that IIR-SOFC fueled by methanol can be well performed as autothermal operation, although slight temperature gradient occurred at the entrance of the reformer chamber. Sensitivity analysis of five important parameters (i.e. operating voltage, reforming catalyst reactivity, inlet steam to carbon ratio, operating pressure and flow direction) was then performed. The increase of operating voltage lowered the average temperature along the reformer chamber and improved the electrical efficiency, but it oppositely reduced the average current density. Greater temperature profile along the system can be obtained by applying the catalyst with lower reforming reactivity; nevertheless, the current density and electrical efficiency slightly decreased. By using high inlet steam to carbon ratio, the cooling spot at the entrance of the reformer can be reduced but both current density and electrical efficiency were decreased. Lastly, with increasing operating pressure, the system efficiency increased and the temperature dropping at the reformer chamber was minimized.