(193g) Generation of Hydrogen from Solid Feedstock Using the Heatpipe Reformer Technology with in-Situ Hydrogen Separation By Nickel Membranes

The Heatpipe Reformer provides an allothermal gasification process for the generation of a hydrogen-rich synthesis gas from solid feedstocks like biomass or lignite. Liquid metal heat pipes transport the heat required for fuel gasification from a fluidized bed furnace to the steam-blown fluidized bed gasification reactor. This allows the generation of a synthesis gas with a hydrogen content of up to 50% and very low nitrogen content. In contrast to other dual fluidized bed processes the completely sealed reformer chamber makes a pressurized process of up to 5 bar(a) possible resulting in a high hydrogen partial pressure and thus driving force for separation. The Institute of Energy Process Engineering (FAU-EVT) therefore follows the approach to apply hydrogen permeable membranes as separation step directly in the reformer. This also allows higher hydrogen yields due to an additional shift of the gasification reactions to the product side as one product is continuously removed.

This work gives an overview on membranes in high temperature applications: It focuses on the temperature range from 750-900°C required for gasification processes. Existing approaches to high temperature hydrogen separation like palladium composite membranes or ceramic materials show advantages and disadvantages mainly regarding stability and prices. The presented approach applies commercial nickel capillary tubes as membranes. Vacuum increases the partial pressure difference between permeate and retentate. This remedies the need for a sweep gas, which is needed with all membranes that cannot withstand a physical pressure difference.

We will present our measurements with a nickel membrane bundle, which was used for a demonstration of the shift of different gas mixtures by hydrogen removal to the product side. The hydrogen removal could significantly enhance CO and CH₄ conversion in the bottle-mixed synthesis gas at an operation temperature of 800°C. The results will show the good compatibility of nickel as membrane material with synthesis gas components like CO, H₂O, CH4, CO₂ and even H₂S. The membranes produced hydrogen with a very high purity of at least 99.9% as expected due to the highly selective solution-diffusion process of the separation.

We will also introduce our measurements with the 100 kW Heatpipe Reformer including results on tar and sulfur content of the generated synthesis gas. The Heatpipe reformer was operated both on lignite and wood pellets, which allows a comparison of these feedstocks with respect to their suitability for hydrogen production.