Modeling and optimal design of cyclic processes for hydrogen purification using hydride-forming metals

Hydrogen at high purity degrees can be obtained by using the well-known Pressure Swing Adsorption (PSA) process. In this paper, a Pressure Swing Absorption (PSAb) alternative operating batch wise is analyzed. An optimal design of cyclic processes for hydrogen purification using hydride-forming metals as absorption material is addressed. The selected case study is a thermo-chemical treatment process that consumes high purity hydrogen to reduce oxides and generates a waste stream that contains residual H2. PSAb process is fed with this hydrogen-poor stream; and high purity hydrogen recovery levels are obtained. A mathematical model based on an energy integrated scheme is presented to develop the optimal process design and to obtain optimal operating conditions. Various optimized solutions are compared by modifying key parameters or restriction equations. Thus, an interesting trade-off between H2 recovery and system size is analyzed. Large systems operate at large cycle times, obtaining up to 98% of H2 recovery in the order of hours, whereas small systems can recover up to 60% of H2 in short cycles of a few seconds.