Sungkwang Lim

Numerical Study on Operating Parameters and Shapes of a Steam Reformer for Hydrogen Production from Methane

Abstract The steam reformer for hydrogen production from methane is studied by a numerical method. Langmuir-Hinshelwood model is incorporated for catalytic surface reactions, and the pseudo-homogeneous model is used to take into account local equilibrium phenomena between a catalyst and bulk gas. Dominant chemical reactions are Steam Reforming (SR) reaction, Water-Gas Shift (WGS) reaction, and Direct Steam Reforming (DSR) reaction. The numerical results are validated with experimental results at the same operating conditions. Using the validated code, parametric study has been numerically performed in view of the steam reformer performance. As increasing a wall temperature, the fuel conversion increases due to the high heat transfer rate. When Steam to Carbon Ratio (SCR) increases, the concentration of carbon monoxide decreases since WGS reaction becomes more active. When increasing Gas Hourly Space Velocity (GHSV), the fuel conversion decreases due to the heat transfer limitation and the low residence time. The reactor shape effects are also investigated. The length and radius of cylindrical reactors are changed at the same catalyst volume. The longer steam reformer is, the better steam reformer performs. However, system energy efficiency decreases due to the large pressure drop. 기호설명 c

Numerical Study on Correlation between Operating Parameters and Reforming Efficiency for a Methane Autothermal Reformer

The objective of this paper is to investigate characteristics of an autothermal reformer at various operating conditions. Numerical method has been used, and simulation model has been developed for the analysis. Pseudo-homogeneous model is incorporated because the reactor is filled with catalysts of a packed-bed type. Dominant chemical reactions are Full Combustion reaction, Steam Reforming(SR) reaction, Water-Gas Shift(WGS) reaction, and Direct Steam Reforming(DSR) reaction. Simulation results are compared with experimental results for code validation. Operating parameters of the autothermal reformer are inlet temperature, Oxygen to Carbon Ratio(OCR), Steam to Carbon Ratio(SCR), and Gas Hourly Space Velocity(GHSV). Temperature at the reactor center, fuel conversion, species at the reformer outlet, and reforming efficiency are shown as simulation results. SR reaction rate is improved by increased inlet temperature. Reforming efficiency and fuel conversion reached the maximum at 0.7 of OCR. SR reaction and WGS reaction are activated as SCR increases. When GHSV is increased, reforming efficiency increases but pressure drop from the increased GHSV may decrease the system efficiency.

고체산화물 연료전지의 전극과 스택운영의 기능적 분석

This study aims to investigate the functional analysis of anode and cathode materials in Anode supported Solid Oxide Fuel Cell. The concentration polarization of single cell was investigated with CFD (Computational Fluid Dynamics) method for the case of the different morphology by using four types of unit cell and discussed to reduce the concentration polarization. The concentration polarization at anode side effected the voltage loss in Anode supported Solid Oxide Fuel Cell and increased contact areas between fuel gas and anode side could reduce the concentration polarization. For intermediate temperature operation, Anode-supported single cells with thin electrolyte layer of YSZ (Yttria-Stabilized Zirconia) were fabricated and short stacks were built and evaluated. We also developed diesel and methane autothermal reforming (ATR) reactors in order to provide fuels to SOFC stacks. Influences of the H₂O/C (steam to carbon ratio), O₂/C (oxygen to carbon ratio) and GHSV (Gas Hourly Space Velocity) on performances of stacks have been investigated. Performance of the stack operated with a diesel reformer was lower than with using hydrogen as a fuel due to lower Nernst voltage and carbon formation at anode side. The stack operated with a natural gas reformer showed similar performances as with using hydrogen. Effects of various reformer parameters such as H₂O/C and O₂/C were carefully investigated. It is found that O₂/ C is a sensitive parameter to control stack performance.

A kinetic model of hydrogen absorption in CeMg12

Abstract Comparing kinetic equations derived from a theoretical model with experimental data published, the kinetic mechanism of hydriding reaction of CeMg12 was analysed. At the initial stage the reaction is controlled by chemisorption of hydrogen on the metal surface and the reacted fraction (F) is expressed as a function of time (t) and temperature (T) F=(1.19 × 10 2 ) (P o − P eq ) T 1 2 exp (−3560 cal/RT )t in the range of 0 ⩽ F ⩽ 0.4. The later stage of the reaction is controlled by another mechanism of metal/hydride interface chemical reaction or hydrogen diffusion in the hydride phase which cannot be clearly distinguished at the moment.

A Study on Operation Characteristics of Planar-type SOFC System Integrated with Fuel Processor

The solid oxide fuel cell (SOFC) is expected to be a candidate for distributed power sources in the next generation, due to its high efficiency and high-temperature waste heat utilization. In this study, the 5-cell SOFC stack was operated with pure hydrogen or reformed gas at anode side and air at cathode side. When stack was operated with diesel and methane ATR reformer, the influence of the and GHSV on performance of stacks have been investigated. The result shows that the cell voltage was decreased with the increase of and due to the partial pressure of fuel and water, and cell voltage was more sensitive to than . Next, the dynamic model of SOFC system included with ATR reformer was established and compared with experimental data. Based on dynamic model, the operation strategy to optimize SOFC-Reformer system was suggested and simulated.

Numerical Thermal and Mass Analyses of Autothermal Reformer

This paper discusses numerical analysis of heat and mass transfer characteristics in autothermal fuel reformer. Assuming local thermal equilibrium between bulk gas and surface of catalyst, one medium approach for energy equation is incorporated. Also, mass transfer between concentrations of bulk gas and near the surface of catalyst is neglected due to relatively low gas mixture velocity. For surface chemical reaction Langmuir-Hinshelwood reaction is incorporated when methane (CH4 ) is reformed to hydrogen-rich gases by autothermal reforming (ATR) reaction. Complete combustion, steam reforming, water gas shift and direct methane steam reforming reactions are included in the chemical reaction model. Under two operating conditions (O/C and S/C), ATR reactions are estimated from the numerical calculations. Mass, momentum, and energy equations are simultaneously calculated with chemical reactions. From the predicted results, we can estimate optimum operating conditions for high hydrogen yield.Copyright

Study on Basic Characteristics of Natural Gas Autothermal Reformer for Fuel Cell Applications

Hydrogen production using current fueling facilities is essential for near-term applications of fuel cells. A preliminary process for developing a natural gas autothermal reforming (ATR) reactor for fuel cells is presented in this paper. A experimental reactor for methane ATR was constructed and used for characterization of Jin reactor. Temperature profiles of the reactor were observed, and reformed gas compositions were analyzed to evaluate efficiency, conversion and reaction heat with varying amounts of at selected furnace temperature and . The amount of showed strong offsets on reactor temperature, efficiency and conversion indicating that is a crucial operation condition. Operation conditions which result in thermal neutrality of ATR reactor system were determined for two cases of an ATR system based on the estimation of enthalpy difference between reactants of assumed inlet temperatures and the products from experimental results. The determined conditions for thermally neutral operations could be used for guidelines to design reformers and for determining the operation parameters of a self sustaining ATR reactor.