Design and operation of a hydrogen purification prototype based on metallic hydrides

Abstract

A hydrogen purification device has been designed and implemented at a prototype scale. The device operation is based on the use of a hydride forming material distributed in two reaction beds, which work in opposition. Under the proposed design, one of the reactors receives the incoming gas, absorbing the hydrogen in it, while the other one desorbs pure hydrogen after a brief venting stage in which contaminants are eliminated. Thus, a continuous flow is processed. The reactors are thermally coupled in order to use the heat of reaction and save energy, working at room temperature without the need of additional heat sources or sinks. The reaction's behavior can be described by a lumped computational model. The model is validated against measured results with pure H2 at different flow rates. This computational tool is used to analyze the system behavior, in terms of hydrogen recovery fraction, under different working conditions, including the presence of trace amounts of CO in the feed gas. Purification experiments are performed using humidified hydrogen where the water vapor content is measured online. As an example scenario, using 300 g of LaNi5 and a gas flow rate of 100 standard cm3/min, the process successfully lowers the humidity content in the gas from 3000 ppmv to 190 ppmv, while achieving a hydrogen recovery fraction of 95%.