Modelling of metal hydride hydrogen compressors from thermodynamics of hydrogen - Metal interactions viewpoint: Part II. Assessment of the performance of metal hydride compressors

Performance of the thermally-driven metal hydride hydrogen compressor (MHHC) is defined by (a) its H-2 compression ratio and maximum output H-2 pressure; (b) throughput productivity/average output flow rate; (c) specific thermal energy consumption which determines H-2 compression efficiency. In earlier studies, the focus of the R&D efforts was on the optimisation of the design of the MH containers and heat and mass transfer in the MH storage and compression systemaimed at shortening the time of the H-2 compression cycle. This work considers an important but insufficiently studied aspect of the development of the industrial-scale thermally driven MHHC's - selection of the materials and optimisation of the materials performance. Further to the operation in the specified pressure/temperature ranges, materials selection should be based on the estimation of the productivity of the compression cycle, and specific heat consumption required for the H-2 compression, which together determine the process efficiency. The current work presents a model to determine productivity and heat consumption for a single- and multi-stage MHHC's which is based on use of Pressure - Composition - Temperature (PCT) diagrams of the utilized metal hydrides at defined operating conditions e temperatures and hydrogen pressures - and main operational features of the MHHC (number of stages, amounts of the MH materials used, cycle time). In Part I of this work [Lototskyy, Yartys, et al., Int J Hydrogen Energy, DOI: 10.1016/j.ijhydene.2020.10.090], we showed that the calculated cycle productivities significantly vary for the different materials. Analysis of the system performance carried out in this work (Part II) shows that the throughput productivity and efficiency of a multi-stage MHHC also depends on the types and amounts of the used MH materials in the multi-stage compressor layout. This has been analysed for a number of the most practically important AB(5) and Laves type AB(2) hydrogen storage alloys integrated into the MHHC's. A comparison of experimentally measured performances of single-, two- and three-stage industrial-scale MHHC's developed by the authors earlier shows their satisfactory agreement with the modelling results thus demonstrating a high value of the presented method for the proper materials selection during development of the MHHC. As an important future development, the work presents a performance evaluation of a two-stage MHHC for H-2 compression operating in the pressure range from 30 to 500 atm at operating temperatures between 20 and 150 degrees C. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The performance of the thermally-driven metal hydride hydrogen compressor is defined by factors such as H-2 compression ratio, maximum output pressure, and throughput productivity. Material selection and performance optimization play a crucial role in enhancing compression efficiency.