Towards a Thermal Optimization of a Methane/Steam Reforming Reactor

Abstract

Plug-flow reactors are very common in methane/steam reforming applications. Their operation presents many challenges, such as a strong dependence on temperature and inlet composition distribution. The strong endothermic steam reforming reaction might result in a temperature drop at the inlet of the reactor. The strong non-uniform temperature distribution due to an endothermic chemical reaction can have tremendous consequences on the operation of the reactor, such as catalyst degradation, undesired side reactions and thermal stresses. One of the possibilities to avoid such unfavorable conditions and control thermal circumstances inside the reforming reactor is to use it as a fuel processor in the solid oxide fuel cell (SOFC) system. The heat generated by exothermic electrochemical SOFC reactions can support the endothermic reforming reaction. Furthermore, the thermal effects of electrochemical reactions help to shape the uniform temperature distribution. To examine thermal management issues, a detailed modeling and corresponding numerical analyses of the phenomena occurring inside the internal reforming system is required. This paper presents experimental and numerical studies on the methane/steam reforming process inside a plug-flow reactor. Measurements including different thermal boundary conditions, the fuel flow rate and the steam-to-methane ratios were performed. The reforming rate equation derived from experimental data was used in the numerical model to predict gas composition and temperature distribution along the steam reforming reactor. Finally, an attempt was made to control the temperature distribution by adopting locally controlled heating zones and non-uniform catalyst density distributions.

An afterburner-powered methane/steam reformer for a solid oxide fuel cells application

“…2 is h 0 wgs = −41.15 kJ mol −1 , which indicates that the reaction is exothermic, however, in comparison with the enthalpy of the reaction (1), the whole process is endothermic. It is assumed that the water-gas shift reaction is in equilibrium in the temperature of the reforming process, thus the reaction rate can be derived from equilibrium equation and partial pressures of species [15] as follows:…”

“…The partial differential equations have been discretized with the Finite Volume Method and the resulting systems of algebraic equations have been solved iteratively with the Gauss-Seidel method. To solve the governing equations, in-house C++ code has been built [15].…”

“…Sciazko with coworkers [23] analyzed the kinetics of methane/steam reforming reaction using the generalized least squares method for SOFC modeling. Mozdzierz et al [15] conducted parametric studies on the methane/steam reforming reaction and concluded that the adaptation of heating zones and localized catalyst density can significantly help in process control.…”

A Multiscale Approach to the Numerical Simulation of the Solid Oxide Fuel Cell

“…The high quality of the waste heat makes it possible to install SOFCs in combined heat and power systems. The high operating temperature also allows for converting electrochemically the carbon monoxide or even to conduct the in-stack internal reforming process, which leads to wide fuel flexibility-the variety of reformed hydrocarbons may be used as a fuel for the SOFC [4][5][6]. Among other advantages there are: low emissions of the greenhouse gases (for the hydrogen-fueled fuel cells virtually there is no emissions) and no emissions of the toxic compounds, relatively high tolerance to fuel impurities [7] and outstanding energy conversion efficiency [2].…”

Identification of Key Transport Phenomena in High-Temperature Reactors: Flow and Heat Transfer Characteristics

“…with a solid oxide fuel cell. [3][4][5] For the process intensification of the reforming reactor itself Bhat et al suggest three principal future directions in their review: 6 catalytic materials, multiscale modeling and a reduction of heat and mass transfer limitations inside the reactor. In the case of SMR the latter was recently addressed mostly through simulations using commercial computational fluid dynamics codes such as Phoenics or Ansys Fluent.…”