Alloy selection for multistage metal-hydride hydrogen compressors: A thermodynamic model. (26th April 2021)

• Record Type: Journal Article
• Authors: Gray, E. MacA.
• Is Part Of: International journal of hydrogen energy. Volume 46:Number 29(2021)
• Page Start: 15702
• Page End: 15715
• Publication Date: 2021-04-26
• Subjects: Hydrogen -- Metal hydride -- Compressor -- Thermodynamics -- van 't Hoff; Hydrogen as fuel -- Periodicals; Hydrogène (Combustible) -- Périodiques; Hydrogen as fuel; Periodicals; 665.81
• DOI: 10.1016/j.ijhydene.2021.02.025
• Languages: English
• ISSNs: 0360-3199

Abstract

Abstract: A thermodynamic model is presented to aid the selection of compatible pairs of hydrogen storage alloys for service in a multi-stage metal-hydride compressor. The model is built around the concept of an ideal compressor in which all pairs of hydrides operate between the same working temperatures. The key feature of the model is a link between the thermodynamic characteristics of the hydrides in each pair (the entropy change Δ S and enthalpy change Δ H when the hydride is formed from the metal) that results from requiring that the heated low-pressure hydride is able to desorb to the cooled high-pressure metal at a unique intermediate pressure. This necessary linking places severe constraints on the choice of alloys, since Δ S and Δ H cannot be freely chosen and are in fact strongly correlated for hydrides with similar operating temperatures. The model is based on the van 't Hoff relation, which is derived from first principles and shown to be only approximately valid at the high hydrogen pressures of interest for vehicle filling stations. Pressure hysteresis and plateau slope are incorporated into the model. A case study of a two-stage compressor is presented, based on the curved van 't Hoff line and the experimentally determined effects of pressure hysteresis and plateau slope. Highlights: A model is developed the linking thermodynamic properties of alloy pairs. Pressure hysteresis and plateau slope are explicitly accounted for. The van 't Hoff line is derived ab initio and shown to be curved at high fugacity. Correlation between enthalpy and entropy change is analysed. A case study and critical review of a real compressor design is presented.