Solar molten salt heated membrane reformer for natural gas upgrading and hydrogen generation: A CFD model

Abstract Parabolic trough solar collectors can be used to drive endothermic reactions, such as methane reforming, while using molten salts as a heat transfer fluid. However, linear focus concentrators can only provide temperatures under 600 °C, resulting in CH4 conversions well below 50%. The equilibrium can be shifted toward much higher conversions if H2 is continuously removed from the reaction mixture via a H2-selective membrane, while simultaneously generating a high-purity H2 stream. In this study, a tube-and-shell, molten salt-heated packed bed membrane reformer (Ni/Al2O3 catalyst, 5 μm supported Pd film membrane) is analyzed numerically using computational fluid dynamics and non-isothermal formulation. The effects of molten salt supply rate and reforming feed flow rate on the reformer performance, which is evaluated in terms of CH4 conversion, H2 recovery, and selectivity to CO, are investigated. Depending on operating parameters, significant temperature and concentration gradients may form in both axial and radial directions. These gradients can be prevented by adjusting feed rates in the reforming and molten salt compartments. For the optimized case, CH4 conversion of 99% and H2 recovery of 87% are predicted for the molten salt feed temperature of 600 °C and reforming feed space velocity of 5000 h−1, which corresponds to a power density of 1.9 kW/L and a fuel heating value upgrade of 40%. A preliminary techno-economic evaluation is provided.

[1]  S. Voutetakis,et al.  Development of a Solar-powered, Fuel-flexible Compact Steam Reformer: the Comethy Project , 2013 .

[2]  G. Froment,et al.  Methane steam reforming: II. Diffusional limitations and reactor simulation , 1989 .

[3]  Jens R. Rostrup-Nielsen.  Conversion of hydrocarbons and alcohols for fuel cells , 2001 .

[4]  J. Armor,et al.  The multiple roles for catalysis in the production of H2 , 1999 .

[5]  C. Keller.  Global Warming 2007. An Update to Global Warming: The Balance of Evidence and Its Policy Implications , 2007, TheScientificWorldJournal.

[6]  A. Paglianti,et al.  Numerical and Experimental Fluid-Dynamic Analysis To Improve the Mass Transfer Performances of Pd−Ag Membrane Modules for Hydrogen Purification , 2010 .

[7]  George Crabtree,et al.  The hydrogen economy , 2006, IEEE Engineering Management Review.

[8]  Shigeyuki Uemiya,et al.  Steam reforming of methane in a hydrogen-permeable membrane reactor , 1990 .

[9]  Joseph Kestin,et al.  Thermophysical properties of fluid D2O , 1984 .

[10]  J. Ely,et al.  Thermophysical Properties of Fluids. II. Methane, Ethane, Propane, Isobutane, and Normal Butane , 1987 .

[11]  M. Balat.  Potential importance of hydrogen as a future solution to environmental and transportation problems , 2008 .

[12]  R. Hughes,et al.  The kinetics of methane steam reforming over a Ni/α-Al2O catalyst , 2001 .

[13]  G. Froment,et al.  Methane steam reforming, methanation and water‐gas shift: I. Intrinsic kinetics , 1989 .

[14]  J. Smith,et al.  Mass transfer, adsorption and reaction in slurry reactors , 1984 .

[15]  P. Breeze.  The Hydrogen Economy , 2017 .

[16]  P. Seferlis,et al.  Modeling and Simulation of a Membrane Reactor for the Low Temperature Methane Steam Reforming , 2013 .

[17]  Christian Sattler,et al.  Solar thermal reforming of methane feedstocks for hydrogen and syngas production—A review , 2014 .

[18]  S. Ted Oyama,et al.  Correlations in palladium membranes for hydrogen separation: A review , 2011 .

[19]  Yuriy Román‐Leshkov,et al.  Computational fluid dynamics study of hydrogen generation by low temperature methane reforming in a membrane reactor , 2015 .

[20]  M. Sheintuch,et al.  On-site pure hydrogen production by methane steam reforming in high flux membrane reactor: Experimental validation, model predictions and membrane inhibition , 2015 .

[21]  Fabiano A.N. Fernandes,et al.  Methane steam reforming modeling in a palladium membrane reactor , 2006 .

[22]  Giampaolo Caputo,et al.  Enriched methane production using solar energy: an assessment of plant performance , 2009 .

[23]  D. Kearney,et al.  Assessment of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field , 2003 .

[24]  G. Holleck.  Diffusion and solubility of hydrogen in palladium and palladium--silver alloys , 1970 .

[25]  M. Wright,et al.  Solar thermal catalytic reforming of natural gas: a review on chemistry, catalysis and system design , 2015 .

[26]  A. Lemonidou,et al.  State-of-the-art catalysts for CH4 steam reforming at low temperature , 2014 .

[27]  B. Younglove,et al.  Thermophysical properties of fluids , 1982 .

[28]  A. Paglianti,et al.  CFD modelling of inorganic membrane modules for gas mixture separation , 2009 .

[29]  M. Romero,et al.  Concentrating solar thermal power and thermochemical fuels , 2012 .

[30]  D. Simakov,et al.  Model‐based optimization of hydrogen generation by methane steam reforming in autothermal packed‐bed membrane reformer , 2011 .

[31]  D. Simakov,et al.  Design of a thermally balanced membrane reformer for hydrogen production , 2008 .

[32]  A. Steinfeld.  Solar thermochemical production of hydrogen--a review , 2005 .

[33]  A. Steinfeld,et al.  Solar-driven gasification of carbonaceous feedstock-a review , 2011 .

[34]  Jianli Hu,et al.  An overview of hydrogen production technologies , 2009 .

[35]  M. De Falco,et al.  Simulation of large-scale membrane reformers by a two-dimensional model , 2007 .

[36]  Giampaolo Caputo,et al.  Solar steam reforming of natural gas for hydrogen production using molten salt heat carriers , 2008 .

[37]  D. Simakov,et al.  Demonstration of a scaled-down autothermal membrane methane reformer for hydrogen generation , 2009 .

[38]  Suttichai Assabumrungrat,et al.  The effect of direction of hydrogen permeation on the rate through a composite palladium membrane , 2000 .

[39]  V. Piemonte,et al.  Solar enriched methane production by steam reforming process: Reactor design , 2011 .

[40]  R. Allen,et al.  A figure of merit assessment of the routes to hydrogen , 2005 .

[41]  B. Djellouli,et al.  Methane Steam Reforming Reaction Behaviour in a Packed Bed Membrane Reactor , 2011 .

[42]  D. Borio,et al.  Two dimensional modeling of a membrane reactor for ATR of methane , 2012 .