Second law optimization of a tubular steam reformer

Abstract We present a numerical method that finds the path of operation that gives minimum total entropy production rate in a tubular steam reformer. The method was applied to the three main reformer reactions in a tubular plug flow reactor with pressure drop and heat exchange. The total entropy production rate was minimized subject to a given production of hydrogen, a fixed inlet pressure, a fixed total molar flow rate at the inlet, and a fixed molar flow rate of inert gas. The inlet and outlet temperatures, the outlet pressure, and the inlet mixture composition were allowed to vary. The temperature profile of the furnace gases was the control variable. Compared to a typical path of operation, we obtained a reduction of more than 60% in the total entropy production rate for the optimal path. The results suggested that a shorter reactor may perform equally well. Interestingly, the optimal path showed regions of either a constant thermal force or a constant chemical force. The new path of operation was not realistic, however, so more work is needed to realise some of the potential gain.

[1]  Ajay K. Ray,et al.  Multiobjective optimization of steam reformer performance using genetic algorithm , 2000 .

[2]  Signe Kjelstrup,et al.  Minimizing the entropy production in heat exchange , 2002 .

[3]  Terje Hertzberg,et al.  Dynamic simulation and optimization of a catalytic steam reformer , 1999 .

[4]  S. K. Ratkje,et al.  Irreversible Thermodynamics: Theory and Applications , 1989 .

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

[6]  S. Kjelstrup,et al.  Minimizing the Entropy Production Rate of an Exothermic Reactor with a Constant Heat-Transfer Coefficient: The Ammonia Reaction , 2003 .

[7]  S. Kjelstrup,et al.  Minimum entropy production rate in plug flow reactors: An optimal control problem solved for SO2 oxidation , 2004 .

[8]  Dick Bedeaux,et al.  Minimizing the Entropy Production of the Methanol Producing Reaction in a Methanol Reactor , 2000 .

[9]  D. Stanciu,et al.  Second Law Analysis of Diffusion Flames , 2001 .

[10]  H. S. Fogler,et al.  Elements of Chemical Reaction Engineering , 1986 .

[11]  秋鹿 研一,et al.  Ammonia : catalysis and manufacture , 1995 .

[12]  P. Mazur,et al.  Non-equilibrium thermodynamics, , 1963 .

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

[14]  Kristian M. Lien,et al.  Equipartition of Forces: A New Principle for Process Design and Optimization , 1996 .

[15]  Ajay K. Ray,et al.  Multi-objective optimization of industrial hydrogen plants , 2001 .

[16]  Jens R. Rostrup-Nielsen,et al.  Catalytic Steam Reforming , 1984 .

[17]  J. Ross,et al.  Some Deductions from a Formal Statistical Mechanical Theory of Chemical Kinetics , 1961 .

[18]  L. Mcgann,et al.  A method whereby Onsager coefficients may be evaluated , 2000 .

[19]  Olav Bolland,et al.  Natural gas fired power plants with CO2-capture-process integration for high fuel-to-electricity conversion efficiency , 2000 .

[20]  Signe Kjelstrup,et al.  Minimizing Entropy Production Rate in Binary Tray Distillation , 2000 .

[21]  K. Denbigh.  The second-law efficiency of chemical processes☆ , 1956 .

[22]  J. C. Schouten,et al.  Design of adiabatic fixed-bed reactors for the partial oxidation of methane to synthesis gas. Application to production of methanol and hydrogen-for-fuel-cells , 2001 .

[23]  Signe Kjelstrup,et al.  Equipartition of forces as a lower bound on the entropy production in heat exchange , 2001 .

[24]  John L. Troutman,et al.  Variational Calculus and Optimal Control , 1996 .

[25]  T. E. Daubert,et al.  Physical and thermodynamic properties of pure chemicals : data compilation , 1989 .