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Journal ArticleDOI

2D heat and mass transfer modeling of methane steam reforming for hydrogen production in a compact reformer

01 Jan 2013-Energy Conversion and Management (Pergamon)-Vol. 65, pp 155-163
TL;DR: In this paper, a 2D heat and mass transfer model is developed to investigate the fundamental transport phenomenon and chemical reaction kinetics in a compact reformer for hydrogen production by methane steam reforming (MSR).
About: This article is published in Energy Conversion and Management.The article was published on 2013-01-01 and is currently open access. It has received 51 citations till now. The article focuses on the topics: Methane reformer & Steam reforming.

Summary (3 min read)

1. Introduction

  • Hydrogen is an ideal energy carrier to support sustainable energy development [1].
  • In the long term, hydrogen can be produced in a clean way by solar thermochemical water splitting, photocatalytic water splitting or water electrolysis driven by solar cells/wind turbines [2,3].
  • In MSR reaction (Eq.1), methane molecules react with steam molecules to produce hydrogen and carbon monoxide in the catalyst layer of reformers.
  • It’s still not very clear how the change in inlet temperature and rate of heat supply can influence the coupled transport and reaction kinetics in the reformer, which are important for optimization of the reformer operation conditions.
  • As the present study do not consider the carbon deposition behavior in the reformer, a constant SCR of 2.0 is adopted.

2. Model development

  • Heat from the combustion duct is supplied to the Ni-based (i.e. [10]) catalyst layer via the solid thin film layer and it is specified as a boundary condition [6].
  • Without considering the 3D effect, the coupled transport and chemical reaction phenomena in the computational domain can be shown in Figure 2, including the solid plate, the reforming duct, and the porous catalyst layer.
  • The chemical model is developed to calculate the rates of chemical reactions and corresponding reaction heats.
  • The CFD model is used to simulate the heat and mass transfer phenomena in the CR.

2.1 Chemical model

  • In operation, methane-containing gas mixture (CH4: 33%; H2O: 67%) is supplied to the reforming duct.
  • The gas species are then transported from the gas duct into the porous catalyst layer, where MSR reaction (Eq. 1) and WGSR (Eq. 2) take place.
  • The formulas proposed by Haberman and Young [11] have been widely used for simulating the rates (mol.m-3.s-1) of MSR ( MSRR ) and WGSR ( WGSRR ), thus is adopted in the present study.
  • The amount of heat generation from WGSR and heat consumption by MSR reaction can be calculated using corresponding enthalpy changes [12].
  • Assuming linear dependence on operating temperature between 600K and 1200K, the reaction heats (J.mol-1) for MSR reaction and WGSR can be calculated as [13].

2.2. Computational Fluid Dynamics (CFD) model

  • Assuming local thermal equilibrium in the porous catalyst layer, the governing equations for mass conservation, momentum conservation, and energy conservation for the whole computational domain are summarized below [14].
  • The Darcy’s law (Eq.26 and 27) is used as source terms in momentum equations (Eqs. (13) and (14)), so that the momentum equations are applicable for both the gas channels and the porous catalyst layers.
  • The source term in energy equation (Eq. (15)) represents reaction heat from the chemical reactions can be calculated by Eq. (28).
  • Detailed descriptions of the source terms can be found in the previous publications [17].

2.3 Numerical scheme

  • The governing equations in the CFD model are solved with the finite volume method (FVM) [14].
  • As a real reformer stack consists of many identical single compact reformers, it is assumed that heat is supplied from the combustion channel (Fig. 1) and there is no heat transfer between compact reformers through the upper boundary (y=yM).
  • The convection terms and diffusion terms are treated with the upwind difference scheme and central difference scheme, respectively.
  • The velocity and pressure are linked with the SIMPLEC algorithm.
  • Computation is repeated until convergence is achieved.

3. Results and discussions

  • The chemical model and CFD model have been validated in the previous publications by comparing the modeling results with data from the literature [17].
  • The dimensions and typical simulation parameters are summarized in Table 2.
  • The following sections focus on parametric simulations to analyze the effects of operating and structural parameters on the coupled transport and reaction kinetics in CR.

3.1 Coupled transport and reaction in a compact reformer for hydrogen production

  • Figure 3 shows the distributions of MSR reaction rates, WGSR rates, temperature, velocity, gas composition (CH4 and H2 as examples) in the compact reformer at an inlet temperature of 1073K, inlet gas velocity of 3m.s-1, and heat supply rate (from the solid plate) of 1kW.m-2.
  • The reaction rates for MSR and WGSR are the highest (25.4 and 14 mol.m-3.s-1 respectively) at the inlet and decrease considerably in the downstream of the reformer (Fig. 3a and 3b).
  • In addition, the temperature is the highest at the inlet (Fig. 3c).
  • A locally low molar fraction of CH4 is also observed near the inlet in the catalyst layer (Fig. 3e).
  • For comparison, the molar fraction of H2 increases along the CR gas flow stream (Fig. 3f).

3.2. Effect of inlet temperature

  • The reaction rates of MSR and WGSR are found to decrease along the main flow stream (Fig. 4a and 4b), but their values are significantly higher than those at 1073K (Fig. 3a and 3b).
  • In addition, the reaction rates decrease more rapidly in the reformer than at 1073K.
  • The high reaction rate of MSR causes the temperature to decrease rapidly along the main flow stream from 1173K at the inlet to about 1040K at the outlet (Fig. 4c).
  • As the reaction rates of MSR and WGSR are higher at 1173K than at 1073K, more CH4 is consumed and more H2 is produced, leading to larger gas composition variation in the reformer (Fig. 4d and 4e).
  • In a word, increasing the inlet temperature increases the reaction rates, temperature gradient, and gas composition variation.

3.4. Effect of inlet gas velocity and microstructure of the catalyst layer

  • It’s found that the reaction rates of MSR and WGSR are the highest at the inlet but decrease considerably along the reformer, due to large temperature drop along the main flow stream.
  • Three-dimensional simulation of chemically reacting gas flows in the porous support structure of an integrated-planar solid oxide fuel cell, Int. J. Heat Mass Transfer 47(2004) 3617-3629. [12].
  • Parameters used in calculating the effective diffusion coefficients [16].

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Citations
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Journal ArticleDOI
TL;DR: A detailed analysis based on the spectroscopic technique revealed that reaction pathways proceeded along a mono-functional or bi-functional mechanism according to the types of active metal and support as mentioned in this paper.
Abstract: Hydrogen production from ethanol is regarded as a promising way for energy sustainable development, which is undergoing an explosive growth over the last decade. Besides operating conditions, hydrogen yield greatly dependent on the nature of metal and the support selected. To date, Rh based catalysts proved to be the most active systems due to the fact that Rh possessed the greatest capacity toward C–C bond cleavage. Support also played a critical role in terms of hydrogen selectivity and stability. MgO, CeO2 and La2O3 etc were evidenced as suitable supports because of their basic characteristic and/or redox capacity. A detailed analysis based on the spectroscopic technique revealed that reaction pathways proceeded along a mono-functional or bi-functional mechanism according to the types of active metal and support. Ethanol dehydrogenation and/or dehydration reaction mainly occurred on the support, and the diffusion/transformation of the intermediates took place at the metal–support interface. Meanwhile, active metal accelerated the decomposition reaction. The observed catalyst deactivation was normally assigned to the coke formation, active metal sintering and/or oxidation as well as the impurity in crude bio-ethanol. Hence, the scope of this review is to address the present progress in ethanol reforming for hydrogen production including catalyst development and the analysis of the reaction mechanism and kinetics in order to shed light on the design of high efficient catalyst systems and the fundamental understanding of ethanol conversion at the molecular level.

230 citations

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional model is developed to simulate the performance of solid oxide fuel cells (SOFCs) fed with CO2 and CH4 mixture, and the electrochemical oxidations of both CO and H2 are included.

97 citations

Journal ArticleDOI
TL;DR: In this article, a local thermal non-equilibrium model is adopted to solve the steady state heat and mass transfer problems of porous media solar receiver, where the fluid entrance surface is subjected to concentrated solar radiation, and CH4/H2O mixture is adopted as feeding gas.

96 citations

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional model for all porous solid oxide button cells is developed for the first time, and the model is then extended for a tubular cell for parametric simulations.

89 citations

Journal ArticleDOI
TL;DR: In this article, the Gibbs free energy minimization method was applied to steam reforming of methane in the ranges of steam to methane from 0.5 to 3, reaction pressure from 1 to 50 bar and operative temperature from 600 to 1200 K. The effect of parameters was determined via an orthogonal second order design.

86 citations

References
More filters
Journal ArticleDOI
TL;DR: In this article, the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production is reviewed, based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range.
Abstract: Nano-sized TiO 2 photocatalytic water-splitting technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy. Presently, the solar-to-hydrogen energy conversion efficiency is too low for the technology to be economically sound. The main barriers are the rapid recombination of photo-generated electron/hole pairs as well as backward reaction and the poor activation of TiO 2 by visible light. In response to these deficiencies, many investigators have been conducting research with an emphasis on effective remediation methods. Some investigators studied the effects of addition of sacrificial reagents and carbonate salts to prohibit rapid recombination of electron/hole pairs and backward reactions. Other research focused on the enhancement of photocatalysis by modification of TiO 2 by means of metal loading, metal ion doping, dye sensitization, composite semiconductor, anion doping and metal ion-implantation. This paper aims to review the up-to-date development of the above-mentioned technologies applied to TiO 2 photocatalytic hydrogen production. Based on the studies reported in the literature, metal ion-implantation and dye sensitization are very effective methods to extend the activating spectrum to the visible range. Therefore, they play an important role in the development of efficient photocatalytic hydrogen production.

3,714 citations


"2D heat and mass transfer modeling ..." refers background or methods in this paper

  • ...Both MSR reaction and water gas shift reaction (WGSR) are considered in the numerical model....

    [...]

  • ...Parametric simulations are performed to examine the effects of various structural/operating parameters, such as porosity, permeability, gas velocity, temperature, and rate of heat supply on the reformer performance....

    [...]

Book
01 Jan 1998

2,172 citations

Journal ArticleDOI
TL;DR: Technical Challenges 4754 4.2.1.
Abstract: 3.8.2. Temperature Distribution Measurements 4749 3.8.3. Two-Phase Visualization 4750 3.8.4. Experimental Validation 4751 3.9. Modeling the Catalyst Layer at Pore Level 4751 3.10. Summary and Outlook 4752 4. Direct Methanol Fuel Cells 4753 4.1. Technical Challenges 4754 4.1.1. Methanol Oxidation Kinetics 4754 4.1.2. Methanol Crossover 4755 4.1.3. Water Management 4755 4.1.4. Heat Management 4756 4.2. DMFC Modeling 4756 4.2.1. Needs for Modeling 4756 4.2.2. DMFC Models 4756 4.3. Experimental Diagnostics 4757 4.4. Model Validation 4758 4.5. Summary and Outlook 4760 5. Solid Oxide Fuel Cells 4760 5.1. SOFC Models 4761 5.2. Summary and Outlook 4762 6. Closing Remarks 4763 7. Acknowledgments 4763 8. References 4763

1,132 citations


"2D heat and mass transfer modeling ..." refers methods in this paper

  • ...The CFD model is used to simulate the heat and mass transfer phenomena in the CR....

    [...]

  • ...206205.5 19.5175MSRH T (10) 45063 10.28WGSRH T (11)...

    [...]

Frequently Asked Questions (2)
Q1. What contributions have the authors mentioned in the paper "2d heat and mass transfer modeling of methane steam reforming for hydrogen production in a compact reformer" ?

In this study, a 2D heat and mass transfer model is developed to investigate the fundamental transport phenomenon and chemical reaction kinetics in a CR for hydrogen production by methane steam reforming ( MSR ). 

The effects of SCR and the catalyst nature on CR performance are not included but will be considered in future works.