1kW SOFC-CHP系统用催化燃烧耦合蒸汽重整反应器的实验研究

针对1 kW 固体氧化物燃料电池热电联供(SOFC-CHP)系统开发了集成催化燃烧、换热及蒸汽重整的反应器,搭建了性能评价系统,系统研究了燃烧侧气体组分及工艺参数对该反应器性能的影响规律。实验结果表明:在反应器燃烧侧气体入口温度为300℃、空燃比为10:1、电堆燃料利用率为65%、水碳比为3 的条件下,重整侧转化率达到73.6%,重整尾气中H₂ 含量为67.5%。电堆燃料利用率对重整反应转化效率影响较大,其值大于80%时,采用尾气燃烧的余热回收方式无法有效为蒸汽重整提供所需热量。在150~350℃范围内,降低燃烧侧气体入口温度对重整反应效率影响较小,建议采用尾气先换热再进行催化燃烧的流程设计,保证重整效率的前提下可有效提升系统热效率。空燃比的降低可小幅度提升重整效率,在保证电堆反应温度稳定的前提下,适当降低空燃比可减少空气压缩机的功耗,从而提升整个系统的效率。研究成果对SOFC-CHP 系统的优化和整体效率提升具有指导意义。     

Investigation of ethanol conversion for hydrogen fuel cells using computer simulations

Ethanol conversion to hydrogen has been investigated by a series of thermodynamic analyses and computer simulations within the context of a cost‐effective fuel processor/fuel cell system where heat exchange is of great importance. Two different methods, multi‐reaction equilibria and Gibbs free energy minimisation, are used for the thermodynamic analyses. The computer simulations consider the catalytic conversion of ethanol to hydrogen on a bimetallic Pt–Ni catalyst by indirect partial oxidation (IPOX) which consists of total oxidation (TOX), steam reforming (SR) and water–gas shift (WGS) reactions. The results indicate that there is an optimal water:fuel ratio for maximum hydrogen production at each operating condition for hydrogen yields calculated as a percentage of the theoretical value. Mass‐based hydrogen yields are also presented considering fuel economy especially for vehicular applications. Finally, the benefits of using a secondary WGS reactor and the comparison of the results of the two thermodynamic methods are highlighted. Copyright © 2005 Society of Chemical Industry     

Model‐based optimization of hydrogen generation by methane steam reforming in autothermal packed‐bed membrane reformer

An autothermal membrane reformer comprising two separated compartments, a methane oxidation catalytic bed and a methane steam reforming bed, which hosts hydrogen separation membranes, is optimized for hydrogen production by steam reforming of methane to power a polymer electrolyte membrane fuel cell (PEMFC) stack. Capitalizing on recent experimental demonstrations of hydrogen production in such a reactor, we develop here an appropriate model, validate it with experimental data and then use it for the hydrogen generation optimization in terms of the reformer efficiency and power output. The optimized reformer, with adequate hydrogen separation area, optimized exothermic‐to‐endothermic feed ratio and reduced heat losses, is shown to be capable to fuel kW‐range PEMFC stacks, with a methane‐to‐hydrogen conversion efficiency of up to 0.8. This is expected to provide an overall methane‐to‐electric power efficiency of a combined reformer‐fuel cell unit of ～0.5. Recycling of steam reforming effluent to the oxidation bed for combustion of unreacted and unseparated compounds is expected to provide an additional efficiency gain. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Effect of Oxygen on Methane Steam Reforming in a Sliding Discharge Reactor

Hydrogen‐rich gas can be efficiently produced in compact plasma reformers by the conversion of a variety of hydrocarbon fuels, including natural gas and gasoline. This article describes experimental and modeling progress in plasma reforming of methane using a sliding discharge reactor (SDR). Experiments have been carried out in a compact device operating at low consumed power (1–2 kW). Previous studies of methane steam reforming using a SDR at atmospheric pressure show promising results (H₂ concentration higher than 55 %). In order to study the effect of oxygen on the methane conversion and thus hydrogen production, a small amount of oxygen in the range of 7–20 % was added to the CH₄‐H₂O mixture. An unexpected result was that under our experimental conditions in the SDR oxygen did not have any influence on the methane conversion. Almost the totality of added oxygen is recovered intact. Moreover, part of the H₂ produced was transformed into water by reaction with O₂. A model describing the chemical processes based on classical thermodynamics is also proposed. The results indicate that the reactor design has to be improved in order to increase conversion and hydrogen production.     

Performance Research on a Methane Compact Reformer Integrated with Catalytic Combustion

A multichannel reformer integrated with catalytic combustion was investigated for methane steam reforming to produce hydrogen. In this system, the main portion of the required heat was supplied by methane oxidation in the catalytic combustor located on two sides of the reformer. In the compact multichannel reactor, the methane conversion rate is high enough compared to the equilibrium values at different temperatures. The performance of the multichannel reformer was investigated under various operating conditions, such as the reformer temperature and the feed stream ratios in both the reformer and the catalytic combustor. The best feed flow rate ratio of reforming to combustion ranged from 1.3 to 1.5, with > 95 % methane conversion. It is anticipated that this multichannel reformer can generate enough hydrogen for a 30‐W fuel cell system, due to its small volume.     

Kinetic and CFD Modeling of Exhaust Gas Reforming of Natural Gas in a Catalytic Fixed-Bed Reactor for Spark Ignition Engines

Fuel reforming is an attractive method for performance enhancement of internal combustion engines fueled by natural gas, since the syngas can be generated inline from the reforming process. In this study, 1D and 2D steady-state modeling of exhaust gas reforming of natural gas in a catalytic fixed-bed reactor were conducted under different conditions. With increasing engine speed, methane conversion and hydrogen production increased. Similarly, increasing the fraction of recirculated exhaust gas resulted in higher consumption of methane and generation of H₂ and CO. Steam addition enhanced methane conversion. However, when the amount of steam exceeded that of methane, less hydrogen was produced. Increasing the wall temperature increased the methane conversion and reduced the H₂/CO ratio.     

基于Fluent的微通道天然气废气重整的数值模拟

利用Fluent软件对微通道反应器中天然气废气重整进行数值模拟。利用甲烷来代替天然气进行模拟。多通道反应器由具有平行通道的堇青石块组成,每个平行通道用Rh/Al_2O_3催化剂洗涂。由于堇青石的低热导率,通道之间的热传递被忽略。研究了进料温度,燃料组成和天然气中存在的丙烷对温度和产物分布的影响。通过模拟结果可得出:开始温度沿着通道良好地分布,并且没有形成明显的热点;增加进料温度有利于甲烷转化和氢气生产,但会导致温度分布不均;提高进料中蒸汽的量有助于增加氢气形成,但轻微地减弱了甲烷转化;提高入口处的O_2/C比值可导致甲烷转化率和温度成比例地增加。     

PEM – Fuel Cell System for Residential Applications

Viessmann is developing a PEM fuel cell system for residential applications. The uncharged PEM fuel cell system has a 2 kW electrical and 3 kW thermal power output. The Viessmann Fuel Processor is characterized by a steam‐reformer/burner combination in which the burner supplies the required heat to the steam reformer unit and the burner exhaust gas is used to heat water. Natural gas is used as fuel, which is fed into the reforming reactor after passing an integrated desulphurisation unit. The low temperature (600 °C) fuel processor is designed on the basis of steam reforming technology. For carbon monoxide removal, a single shift reactor and selective methanisation is used with noble metal catalysts on monoliths. In the shift reactor, carbon monoxide is converted into hydrogen by the water gas shift reaction. The low level of carbon monoxide at the outlet of the shift reactor is further reduced, to approximately 20 ppm, downstream in the methanisation reactor, to meet PEM fuel cell requirements. Since both catalysts work at the same temperature (240 °C), there is no requirement for an additional heat exchanger in the fuel processor. Start up time is less than 30 min. In addition, Viessmann has developed a 2 kW class PEFC stack, without humidification. Reformate and dry air are fed straight to the stack. Due to the dry operation, water produced by the cell reaction rapidly diffuses through the electrolyte membrane. This was achieved by optimising the MEA, the gas flow pattern and the operating conditions. The cathode is operated by an air blower.     

A hybrid adsorbent-membrane reactor (HAMR) system for hydrogen production

Design characteristics and performance of a novel reactor system, termed a hybrid adsorbent-membrane reactor (HAMR), have been investigated for hydrogen production. The recently proposed HAMR concept couples reactions and membrane separation steps with adsorption on the membrane feed-side or permeate-side. Performance of conventional reactors has been significantly improved by this integrated system. In this paper, an HAMR system has been studied involving a hybrid-type packed-bed catalytic membrane reactor undergoing methane steam reforming through a porous ceramic membrane with a CO₂ adsorption system. This HAMR system is of potential interest to pure hydrogen production for fuel cells for various mobile and stationary applications. Reactor behaviors have been investigated for a range of temperature and pressure conditions. The HAMR system shows enhanced methane conversion, hydrogen yield, and product purity, and provides good promise for reducing the hostile operating conditions of conventional reformers, and for meeting the product purity requirements.     

Mathematical Modeling and Optimization of Combined Steam and Dry Reforming of Methane Process in Catalytic Fluidized Bed Membrane Reactor

Mathematical modeling of the methane-combined reforming process (steam methane reforming–dry reforming methane) was performed in a fluidized bed membrane reactor. The model characterizes multiple phases and regions considering low-density phase, high-density phase, membrane, and free board regions that allow study of reactor performance. It is demonstrated that the combined effect of membrane and reaction coupling provides opportunities to overcome equilibrium limits and helps to achieve higher conversion. Additionally, the influence of key parameters on reactor performance including reactor temperature, reactor pressure, steam to methane feed ratio (S/C), and carbon dioxide to methane feed ratio (CO₂/C) were investigated in the multi-objective genetic algorithm to find the optimal operating conditions. Finally, the process of steam reforming was simulated in selected optimal conditions and the results are compared to those of the combined reforming process. Comparison reveals the superiority of the combined reforming process in terms of methane conversion, catalyst activity, and outlet H₂/CO ratio in the syngas product in being close to unity.     

Methane steam reforming modeling in a palladium membrane reactor

A mathematical model of a membrane reactor used for methane steam reforming was developed to simulate and compare the maximum yields and operating conditions in the reactor with that in a conventional fixed bed reactor. Results show that the membrane reactor resents higher methane conversion yield and can be operated under milder conditions than the fixed bed reactor, and that membrane thickness is the most important construction parameter for membrane reactor success. Control of the H₂:CO ratio is possible in the membrane reactor making this technology more suitable for production of syngas to be used in gas-to-liquid processes (GTL).     

基于化学链燃烧的吸收剂引导的焦炉煤气水蒸气重整制氢过程模拟

建立了基于化学链燃烧供能的吸收剂引导的焦炉煤气水蒸气重整制氢系统,该系统包含吸收剂引导的焦炉煤气重整反应器（SECOGSR）、燃料反应器和空气反应器。该系统能产生高纯H₂［93.23%（mol）］,仅通过冷凝即可实现CO₂的捕获,分离能耗低。采用Aspen Plus软件对吸收剂引导的焦炉煤气重整制氢过程进行了模拟,得到优化的反应条件为：温度650℃,压力1.5 MPa,Ca/C=1,H₂O/C=4。并对系统进行了模拟,以NiO/Y₂O₃/ZrO₂(0.73/0.022/0.248,摩尔比）为化学链燃烧的载氧体和载能体,在满足反应器自热平衡和系统吸放热平衡的基础上,重整1mol焦炉煤气,燃料反应器和空气反应器所需的焦炉煤气、空气及载氧体NiO/Y₂O₃/ZrO₂的量分别为0.139、0.648、3.11 mol。该系统消耗1 mol焦炉煤气的产H₂量为1.30 mol,捕获的CO₂的量为0.355 mol。     

Toward autothermal and hydrogen‐producing sorbent regeneration for calcium‐looping

This paper presents a simulation study on the kinetic performance of combined methane combustion, steam/dry reforming, and limestone calcination for autothermal, hydrogen‐producing, and rapid sorbent regeneration in turbulent fluidized bed reactors. The effects of key operational factors are investigated at reactor pressures of 1 bar to 5 bars, including reactor temperature, CaCO₃/total gas molar feed ratio, and sorbent residence time. The results are compared to those for conventional steam calciners, demonstrating the potential for superior performance of this novel sorbent regeneration technology under certain circumstances. A simple, but effective, design methodology is then suggested to determine the proper range of operating conditions and/or reactor dimensions for limestone calcination using this process.     

Methane steam reforming at microscales: Operation strategies for variable power output at millisecond contact times

The potential of methane steam reforming at microscale is theoretically explored. To this end, a multifunctional catalytic plate microreactor, comprising of a propane combustion channel and a methane steam reforming channel, separated by a solid wall, is simulated with a pseudo 2‐D (two‐dimensional) reactor model. Newly developed lumped kinetic rate expressions for both processes, obtained from a posteriori reduction of detailed microkinetic models, are used. It is shown that the steam reforming at millisecond contact times is feasible at microscale, and in agreement with a recent experimental report. Furthermore, the attainable operating regions delimited from the materials stability limit, the breakthrough limit, and the maximum power output limit are mapped out. A simple operation strategy is presented for obtaining variable power output along the breakthrough line (a nearly iso‐flow rate ratio line), while ensuring good overlap of reaction zones, and provide guidelines for reactor sizing. Finally, it is shown that the choice of the wall material depends on the targeted operating regime. Low‐conductivity materials increase the methane conversion and power output at the expense of higher wall temperatures and steeper temperature gradients along the wall. For operation close to the breakthrough limit, intermediate conductivity materials, such as stainless steel, offer a good compromise between methane conversion and wall temperature. Even without recuperative heat exchange, the thermal efficiency of the multifunctional device and the reformer approaches ～65% and ～85%, respectively. © 2008 American Institute of Chemical Engineers AIChE J, 2009     

Simulation of autothermal reforming in a staged‐separation membrane reactor for pure hydrogen production

Steam methane reforming with oxygen input is simulated in staged‐separation membrane reactors. The configuration retains the advantage of regular membrane reactors for achieving super‐equilibrium conversion, but reaction and membrane separation are carried out in two separate units. Equilibrium is assumed in the models given the excess of catalyst. The optimal pure hydrogen yield is obtained with 55% of the total membrane area allocated to the first of two modules. The performance of the process with pure oxygen input is only marginally better than with air. Oxygen must be added in split mode to reach autothermal operation for both reformer modules, and the oxygen input to each module depends on the process conditions. The effects of temperature, steam‐to‐carbon ratio and pressure of the reformer and the area of the membrane modules are investigated for various conditions. Compared with a traditional reformer with an ex situ membrane purifier downstream, the staged reactor is capable of much better pure hydrogen yield for the same autothermal reforming operating conditions.     

ONBOARD FUEL CONVERSION FOR HYDROGEN-FUEL-CELL-DRIVEN VEHICLES

Increasingly stringent legislation controls emissions from internal combustion engines to the point where alternative power sources for vehicles are necessary. The hydrogen fuel cell is one promising option, but the nature of the gas is such that the conversion of other fuels to hydrogen on board the vehicle is necessary.

The conversion of methanol, methane, propane, and octane to hydrogen is reviewed. A combination of oxidation and steam reforming (indirect partial oxidation) or direct partial oxidation are the most promising processes. Indirect partial oxidation involves combustion of part of the fuel to produce sufficient heat to drive the endothermic steam reforming reaction. Direct partial oxidation is favored only at high temperatures and short residence times but is highly selective. However, indirect partial oxidation is shown to be the preferred process for all fuels.

The product gases can be taken through a water–gas shift reactor, but still retain ～2% carbon monoxide, which poisons fuel-cell catalysts. Selective oxidation is the preferred route to removal of residual carbon monoxide. Low-temperature oxidation in the absence and presence of an excess of hydrogen is reviewed. Au-based catalysts show much promise, but precious metal catalysts such as Pt/zeolite have some advantages.     

Development of a Combined Plasma-Matrix Reformer for Solid Oxide Fuel Cell Application

A novel plasma-matrix reformer (PMR) was suggested for methane conversion into hydrogen-rich fuel. To demonstrate the possibility of reforming performance, characteristics of product gas and CH₄ conversion were identified according to O₂/C ratio, water vapor supply, reformed gas recirculation, and water feed in the recirculation gas affecting energy conversion and hydrogen production. When the reformed gas recirculation and water feed to the recirculation pipe were performed at the same time, hydrogen production and energy conversion efficiency were superior compared to the conventional reforming method. The optimal operating conditions of the PMR were determined. The obtained high energy conversion efficiency and hydrogen selectivity indicated the applicability to solid oxide fuel cell stacks for residential power generation.     

Modeling of a metal monolith catalytic reactor for methane steam reforming-combustion coupling

A novel metal monolith reactor for coupling methane steam reforming with catalytic combustion is proposed in this work, the metal monolith is used as a co-current heat exchanger and the catalysts are deposited on channel walls of the monolith. The transport and reaction performances of the reactor are numerically studied utilizing heterogeneous model based on the whole reactor. The influence of the operating conditions like feed gas velocity, temperature and composition are predicted to be significant and they must be carefully adjusted in order to avoid hot spots or insufficient methane conversion. To improve reactor performance, several different channel arrangements and catalyst distribution modes in the monolith are designed and simulated. It is demonstrated that reasonable reactor configuration, structure parameters and catalyst distribution can considerably enhance heat transfer and increase the methane conversion, resulting in a compact and intensified unit.     

Experimental Study of Internal Reforming on Large‐area Anode Supported Solid Oxide Fuel Cells

The effect of endothermic internal steam reformation of methane and exothermic fuel cell reaction on the temperature of a planar‐type anode‐supported solid oxide fuel cell was experimentally investigated as a function of current density and fuel utilization. We fabricated a large‐area (22 × 33 cm²) cell and compared temperature profiles along the cell using 30 thermocouples inserted through the cathode end plate at 750 °C under various conditions (Uf ∼50% at 0.4 A cm⁻²; Uf ∼70% at 0.4 A cm⁻²; Uf ∼50% at 0.2 A cm⁻²) with hydrogen fuel and methane‐steam internal reforming. The endothermic effect due to internal reforming mainly occurs at the gas inlet region, so this process is not very effective to cool down the hot spot created by the exothermic fuel cell reaction. This eventually results in a larger temperature difference on the cell. The most moderate condition with regards to thermal gradient on the cell corresponds to high fuel utilization (Uf ∼70%) and low current density (∼0.2 A cm⁻²). The electrochemical performance was also measured, and it was found that the current–voltage characteristics are comparable for the cell operated under hydrogen fuel and internal steam reforming of methane because of lower polarization resistance with high partial pressure of water vapor.     

Sorption enhanced steam reforming (SESR): a direct route towards efficient hydrogen production from biomass‐derived compounds

OVERVIEW: Efficient conversion of biomass to hydrogen is imperative in order to realize sustainable hydrogen production. Sorption enhanced steam reforming (SESR) is an emerging technology to produce high purity hydrogen directly from biomass‐derived oxygenates, by integrating steam reforming, water‐gas shift and CO₂ separation in one‐stage. Factors such as simplicity of the hydrogen production process, flexibility in feedstock, high hydrogen yield and low cost, make the SESR process attractive for biomass conversion to fuels. IMPACT: Recent work has demonstrated that SESR of biomass‐derived oxygenates has greater potential than conventional steam reforming for hydrogen production. The flexibility of SESR processes resides in the diversity of feedstocks, which can be gases (e.g. biogas, syngas from biomass gasification), liquids (e.g. bioethanol, glycerol, sugars or liquid wastes from biomass processing) and solids (e.g. lignocellulosic biomass). SESR can be developed to realize a simple biomass conversion process but with high energy efficiency. APPLICATIONS: Hydrogen production by SESR of biomass‐derived compounds can be integrated into existing oil refineries and bio‐refineries for hydrotreating processing, making the production of gasoline and diesel greener. Moreover, hydrogen from SESR can be directly fed to fuel cells for power generation. Copyright © 2012 Society of Chemical Industry