Endothermic catalytic reaction apparatus, for converting hydrocarbon feedstock to hydrogen-rich gases, has attracted increasing attention in recent years [1, 2]. Commercial production of hydrogen is commonly achieved by a process known as steam reforming [3], that involves the endothermic reaction between a mixture of hydrocarbon feedstock and steam passed through a catalyst filled reactor tubing that is heated [4]. In commercial steam reformers for large-scale production of hydrogen from hydrocarbon feeds, endothermic heat is commonly supplied by the combustion of carbonaceous fuel and oxidant in a diffusion or turbulent flame burner that radiates to the refractory walls of a combustion chamber [5], thereby heating them to incandescence, and providing a radiant source for heat transfer to a tubular reaction chamber [6]. Uniform radiation to the surfaces of the tubular reaction chamber is essential since excessive local overheating of the tube surface can result in mechanical failure [6]. In large-scale commercial steam reformers, mal-distribution of heat within the furnace chamber is minimized by providing large spacing between the individual reactor tubes, the furnace walls, and the burner flames [7, 8]. However, for small-scale catalytic reaction apparatus that is uniquely compact, such as for the production of hydrogen for small fuel cell applications, special design features are needed to prevent tube overheating.

A compact reformer comprises an annular reaction chamber concentrically disposed around an internal burner chamber containing a vertically disposed cylindrical radiant burner that uniformly radiates in the radial direction [5, 6]. A uniform radiation pattern to a concentrically disposed annular reaction chamber that surrounds the radiant burner, is provided, thereby avoiding the problems with flame impingement and local overheating of tube surfaces that are associated with the use of diffusion or turbulent flame burners in compact reformer apparatus [7, 8]. However, there are practical limitations regarding the use of an annular reaction chamber for small-scale reformers having hydrogen production rates of less than about 1500 standard cubic foot per hour. The heat transfer coefficient of gaseous reactants contained within an annular reaction chamber is directly related to the velocity of the gaseous reactants within the annular space [9, 10]. In order to limit the reaction chamber wall temperature, the velocity of gaseous reactants within the annular space must be sufficiently high to absorb the radiant heat flux that impinges on the reaction chamber tube walls [11, 12]. However, for very small-scale reformers, this requires that the width of the annular reaction chamber space be small [13, 14]. It is common practice to limit the maximum diameter of the catalyst particles packed within an annular space to less than 20 percent of the width of the annular space [15, 16] in order to ensure that the catalyst is evenly distributed within the reaction chamber and to prevent gas channeling along the walls of the reaction chamber [17, 18]. However, for an annulus having a small width dimension, this requires use of catalyst particles of particularly small diameters thereby resulting in an undesirably high pressure drop through the catalyst bed.

The benefits of a flameless radiant burner for use in compact catalytic reaction apparatus of annular reaction chamber geometry are known [19, 20]. For small-scale reformer applications, a tubular reaction chamber geometry is preferred over annular reaction chamber geometry in order to simultaneously achieve high heat transfer coefficients and low pressure drops within the reaction chamber [21, 22]. There is need for a compact endothermic catalytic reaction apparatus to achieve the objects of compact design, while avoiding the problems of flame impingement, excessive reaction chamber wall temperatures, and excessive reaction chamber pressure drop by application of a tubular reaction chamber that is heated by the radiant burner [23, 24]. The tubular endothermic reaction chamber may employ a combination of catalyst particle sizes and reactant mass velocities to control the reactor pressure drop and the maximum reaction chamber tube wall temperature within certain needed limits [25, 26]; and the radiant burner is operated at specific ranges of combustion intensity and excess air to control surface temperature of the radiant burner within certain needed limits [27, 28]. The design extends the practical range of tubular endothermic reaction chamber geometry that can be used in combination with radiant burners for converting hydrocarbon feedstock to useful industrial gases.

Many chemical processes utilize catalysts to enhance chemical conversion behavior. A catalyst promotes the rate of chemical conversion but does not affect the energy transformations which occur during the reaction. The present study is focused primarily upon the performance and efficiency analysis of steam-methanol reforming processes in combined parallel plate heat exchanger-reactors. The steady-state continuity, momentum, energy, and species conservation equations are solved in the fluid phase and the heat equation is solved in the solid phase using a finite volume approach. An adaptive meshing scheme is used for the discretization of the differential equations. Computational fluid dynamics simulations are carried out over a wide range of material conductivities. Continuity in temperature and heat flux is applied at the fluid-solid interfaces. Neither heat-transfer nor mass-transfer correlations are employed. Parallel processing employing a message passing interface is used to speed up the most demanding calculations. The present study aims to explore how to effectively enhance chemical conversion behavior by utilizing catalysts. Particular emphasis is placed upon the effect of wall thermal conductivity on the performance and efficiency of steam-methanol reforming processes in combined parallel plate heat exchanger-reactors.