(424c) Measured and Modeled Properties of Radial Microchannel Reactors (RMR)

Efficient catalytic conversion of hydrocarbons to hydrogen and/or synthesis gas remains a critical challenge for both emerging clean energy industries and existing petrochemical and natural gas markets. This paper presents a “Radial Microchannel Reactor” (RMR) architecture developed by Power & Energy, Inc. for manufacturing highly compact steam reformers capable of achieving comparable overall power densities to existing autothermal reformers (ATRs) at reduced catalyst loadings and high space velocities [1]. The RMR system is manufactured via laser welding techniques originally developed by P&E for constructing highly compact gas purification systems. Each microchannel is formed from the annular gap between two nested small tubes, typically designed to have a gap width between 300 and 700 microns. The outer tube is closed at one end and welded into manifold ‘A’ at its other end. The inner tube has one end, close to the closed end of the outer tube and other end welded to manifold ‘B’. More than 1,000 such individual RMR assemblies may be integrated in parallel using a close packed hexagonal pattern in an 8” diameter manifold. This network of RMR assemblies is suspended in a single combustion volume suitable for atmospheric ignition of fuel and air during startup while enabling a smooth transition to catalytic combustion at the outer tube surfaces at steady-state. Catalytic combustion on the outer surface of each RMR provides efficient transfer of combustion heat to the reforming reaction on the inner surface of the outer tube.

            This presentation will detail bench-scale experiments for evaluating heat transfer and reaction rates of a single microchannel thermally separated into 3 sections, each 1.25” in length. The inner surface of the larger tube is coated with a nickel-based steam reforming catalyst (~58mg) and an insert tube is coaxially mounted within the bore to complete the RMR geometry. This enables detailed studies of reaction dynamics of the fuel, steam and catalyst issues in a test setup that has the same internal features for the reforming catalyst as a production based RMR system. This apparatus provides heat flow measurements to individual sections of a single microchannel held at constant temperature and is used to measure the power requirements along the outer surface of the individual RMR channel sections to ensure an inner wall temperature of 750^oC. Experimental data with methane steam reforming catalyst with a channel gap of 300 microns was obtained over a range of inlet gas space velocities in terms of the net power absorbed by the reforming reaction to maintain reactor-wall temperature. For the single RMR described here, heat duties approaching 40W correspond to a volumetric heat flux of > 800W/cm³, more than an order of magnitude improvement over competing planar designs. Experimental data is employed to validate computational fluid-dynamic (CFD) models of the RMR system, which are subsequently employed to optimize catalyst distributions and explore thermal integration strategies.

[1] Wilhite, B.A.; L. Breziner; J. Mettes; P. Bossard. Radial Microchannel Reactors (RMR) for Efficient, Compact Steam Reforming of Methane: Experimental Demonstration and Design Simulations, Energy & Fuels, in press (2013).