Joonguen Park

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 Analysis of the Heat and Mass Transfer Characteristics in an Autothermal Methane Reformer

This paper discusses a numerical analysis of the heat and mass transfer characteristics in an autothermal methane reformer. Assuming local thermal equilibrium between the bulk gas and the surface of the catalyst, a one-medium approach for the porous medium analysis was incorporated. Also, the mass transfer between the bulk gas and the catalysts surface was neglected due to the relatively low gas velocity. For the catalytic surface reaction, the Langmuir-Hinshelwood model was incorporated in which methane (CH 4 ) is reformed to hydrogen-rich gases by the autothermal reforming (ATR) reaction. Full combustion, steam reforming, water-gas shift, and direct steam reforming reactions were included in the chemical reaction model. Mass, momentum, energy, and species balance equations were simultaneously calculated with the chemical reactions for the multiphysics analysis. By varying the four operating conditions (inlet temperature, oxygen to carbon ratio (OCR), steam to carbon ratio, and gas hourly space velocity (GHSV)), the performance of the ATR reactor was estimated by the numerical calculations. The SR reaction rate was improved by an increased inlet temperature. The reforming efficiency and the fuel conversion reached their maximum values at an OCR of 0.7. When the GHSV was increased, the reforming efficiency increased but the large pressure drop may decrease the system efficiency. From these results, we can estimate the optimal operating conditions for the production of large amounts of hydrogen from methane.

Numerical Analysis of a Steam Reformer Coupled With a Combustion Burner

This study focuses on a numerical simulation of a steam reforming system. The steam reforming system consisted of a cylindrical steam reformer and a combustion burner. The heat was supplied to an endothermic steam reformer from combustion gases. The correlation between the performance and the shape of the system was studied using two different configurations. The first configuration utilized a flame guide between the combustion burner and the steam reformer, whereas the other did not. The flame guide changed the flow of the combustion gas, which affected the heat transfer rate from the burner to the reformer. Reactor temperature profiles, heat transfer rates, fuel conversions, and hydrogen yields were calculated. In addition, the fuel feed ratio between the burner and the steam reformer was manipulated as an operating parameter.

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.

Numerical Simulation of Operating Parameters in a Methane Fueled Steam Reforming Reactor

This paper studies the heat and mass transfer characteristics in a steam reforming reactor using numerical simulation and investigates the operating parameters for effective hydrogen production. Simultaneous analysis of governing equations and chemical reaction equations is carried out in a multiphysical simulation. The major reactions are assumed to be the steam reforming, water-gas shift (WGS), and direct steam reforming reactions. The temperature and species concentrations measured for the experiment are compared with numerical results. After validation of the developed code, numerical work is carried out to study correlations between the performance and Operating parameters, which are the wall temperature, the inlet temperature, the steam to carbon ratio (SCR), and the gas hourly space velocity (GHSV). The fuel conversion increases with the high wall temperature due to the increased heat transfer. The inlet temperature may not affect the fuel conversion, if the reformer length is long enough. However, the heat transfer limitation can occur near the inlet when the inlet temperature is over 300°C. The concentration of carbon monoxide becomes lower with increasing SCR due to the decreased WGS reaction rate. The high GHSV causes the short residence time and it is the reason for the low fuel conversion.

Numerical Modeling of Physical Property and Electrochemical Reaction for Solid Oxide Fuel Cells

초록:고체산화물연료전지는세라믹물질로이루어지며,세라믹물질의물성치는작동조건에따라달라진다.따라서,높은신뢰성을가지는시뮬레이션모델을개발하기위해서는세라믹물질의물성치를정확하게예측할수있어야한다.본논문에서는고체산화물연료전지의성능에영향을미치는여러가지물성치를선택하고그물성치를위한시뮬레이션모델이개발되었다.개회로전압을위한깁스에너지,활성화손실을위한교환전류밀도,저항손실을위한전기전도도가계산되었다.또한,다공성전극내부의물질전달해석을위해서분자확산과누센확산을함께고려하는유효확산계수가계산되었다.이러한계산과정후에물성치모델과전기화학반응모델이동시에시뮬레이션되었다.해석코드의검증을위해서전산해석결과는실험결과및Chan등에의해서수행된이전연구결과와비교되었다.Abstract: Solid oxide fuel cells (SOFCs) are commonly composed of ceramic compartments, and it is known that thephysical properties of the ceramic materials can be changed according to the operating temperature. Thus, the physicalproperties of the ceramic materials have to be properly predicted to develop a highly reliable simulation model. In thisstudy, several physical properties that can affect the performance of SOFCs were selected, and simulation models for thosephysical properties were developed using our own code. The Gibbs free energy for the open circuit voltage, exchangecurrent densities for the activation polarization, and electrical conductivity for the electrolyte were calculated. In addition,the diffusion coefficient—including the binary and Knudsen diffusion mechanisms—was calculated for mass transportanalysis at the porous electrode. The physical property and electrochemical reaction models were then simulatedsimultaneously. The numerical results were compared with the experimental results and previous works studied by Chan etal. for code validation.

Numerical Study on the Performance and the Heat Flux of a Coaxial Cylindrical Steam Reformer for Hydrogen Production

Heat transfer rate is a very important factor for the performance of a steam reformer because a steam reforming reaction is an endothermic reaction. Coaxial cylindrical reactor is the reactor design which can improve the heat transfer rate. Temperature, fuel conversion and heat flux in the coaxial cylindrical steam reformer are studied in this paper using numerical method under various operating conditions. Langmuir-Hinshelwood model and pseudo-homogeneous model are incorporated for the catalytic surface reaction. Dominant chemical reactions are assumed as a Steam Reforming (SR) reaction, a Water-Gas Shift (WGS) reaction, and a Direct Steam Reforming (DSR) reaction. Although coaxial cylindrical steam reformer uses 33% less amount of catalyst than cylindrical steam reformer, its fuel conversion is increased 10 % more and its temperature is also high as about 30 degree. There is no heat transfer limitation near the inlet area at coaxial-type reactor. However, pressure drop of the coaxial cylindrical reactor is 10 times higher than that of cylindrical reactor. Operating parameters of coaxial cylindrical steam reformer are the wall temperature, the inlet temperature, and the Gas Hourly Space Velocity (GHSV). When the wall temperature is high, the temperature and the fuel conversion are increased due to the high heat transfer rate. The fuel conversion rate is increased with the high inlet temperature. However, temperature drop clearly occurs near the inlet area since an endothermic reaction is active due to the high inlet temperature. When GHSV is increased, the fuel conversion is decreased because of the heat transfer limitation and short residence time.

Mass Transfer Analysis of Metal-Supported and Anode-Supported Solid Oxide Fuel Cells

Metal-supported solid oxide fuel cells (SOFCs) have been developed to commercialize SOFCs. This new type of SOFC has high mechanical strength, but its mass transfer rate may be low due to the presence of a contact layer. In this study, the mass transfer characteristics of an anode-supported SOFC and a metal-supported SOFC are studied by performing numerical simulation. Governing equations, electrochemical reactions, and ceramic physical-property models are determined simultaneously; molecular diffusion and Knudsen diffusion are considered in mass transport analysis of porous media. The experimental results are compared with simulation data to validate the results of numerical simulation. The average current density of the metal-supported SOFC is 23% lower than that of the anode-supported SOFC. However, because of the presence of the contact layer, the metal-supported SOFC has a more uniform distribution than the anode-supported SOFC.

Investigation of a Steam Reforming System of Methane Integrated With a Combustion Burner

The objective of this study is to analyze the steam reforming system using numerical method. The system consists of a cylindrical-type steam reformer and a combustion burner. Heat is supplied to the endothermic steam reformer by the combustion gases which flow around the reformer. Eddy Break-Up (EBU) model is incorporated for the combustion reaction, and pseudo-homogeneous model is used for the steam reforming reaction. The temperature at the reformer center and the concentration of species at the outlet are compared with the measured data for code validation. The correlation between the performances and the shapes of the system has been studied by using two different configurations. One has the flame guide between the combustion burner and the steam reformer, and the other does not. The flame guide makes the flow of the combustion gas changed. The operating parameters are reactant flow rates which are supplied to the steam reformer and the combustion burner. Reactor temperature profiles, heat transfer rates, fuel conversion, and the hydrogen yields are calculated as the numerical results. Moreover, fuel feed ratio between the burner and the reformer is also manipulated as an operating parameter to discuss about efficiency.Copyright