Nickel membranes for in-situ hydrogen separation in high-temperature fluidized bed gasification processes

Abstract

The Heatpipe Reformer provides an allothermal gasification process for the generation of hydrogen-rich synthesis gas. This synthesis gas can be used for generation of hydrogen for applications like fuel cells, engines, storage or the chemical industries. Conventional processes for hydrogen production involve CO Shift reactors to enhance hydrogen yield followed by hydrogen separation using gas scrubbing technology. The Institute of Energy Process Engineering (FAU-EVT) 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 paper gives an overview on membranes in high temperature applications. It focuses on the temperature range from 750 to 900 °C required for biomass 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.In the experimental section several commercial nickel capillaries were tested for their hydrogen permeability and the results from a parameter study regarding the influence of synthesis gas components like CO, CH4 and H2O on permeation are shown. The nickel membranes were also tested in hydrogen containing H2S, which can be present in synthesis gas in concentrations of up to 1000 ppm.