Potential of Using Graded Porous Stainless Steel Support Structures to Improve Energy Efficiency of Hydrogen Separation in Steam Reforming Process

Abstract

This study investigates the potential of using graded porous stainless steel (PSS) support structures to reduce the cost and size of membrane hydrogen separation units and maximize hydrogen production from steam reforming processes. Palladium (Pd) alloy composite membranes offer potential to reduce costs associated with distributed steam reforming by producing nearly pure hydrogen more efficiently and compactly than conventional separation methods. Typical membrane separator units consist of a thin Pd layer deposited on a PSS support structure. Due to the high cost of palladium, it is desired to minimize the amount used while also ensuring membrane reliability. The thickness of the deposited layer is largely determined by pore sizes on the surface of the support and can vary from 2 to 20 μm. Typical PSS support configuration includes a fine (1-10 μm pore radius) layer and one or two coarse (>10 μm) layers fabricated with selective laser sintering. Recent advances in additive manufacturing methods offer the potential to produce lower-cost PSS supports in which more finely graded pore size distributions can be produced. An analytical mass transfer model is developed to assess the impact of these different geometries on membrane unit performance for representative operating conditions. Preliminary results suggest improvements to the support geometry may increase hydrogen recovery by up to 20% for a given surface area.