Simulation and design of a three-stage metal hydride hydrogen compressor based on experimental thermodynamic data

Abstract

A semi-empirical method was developed to design a three stage Metal Hydride Hydrogen Compressor (MHHC) through the determination of thermodynamic properties of several hydrides. As a first step, three AB 2 -type alloys that satisfy operation conditions were selected from published thermodynamic data entailing over 200 single plateau hydrides. These alloys were synthetized by arc melting and characterized by X-Ray Powder Diffraction (XRPD), Scanning Electron Microscopy (SEM) and Energy Dispersion X-ray spectroscopy (EDX). Absorption and desorption Pressure-composition-Isotherms (P-c-I) were determined between 23 and 80 ºC to characterize their thermodynamic properties. Subsequently, an algorithm that uses these experimental data and a real equation of state for gaseous H 2 was implemented to simulate the volume, alloy mass, pressure and temperature of operation for each compressor stage, while optimizing the compression ratio and total number of compressed H 2 moles. Optimal desorption temperatures for the three stages were identified within the range of 110 to 132 °C. A system compression ratio (CR) of 92 was achieved. The number of H 2 moles compressed, the alloy mass and volume of each stage depend linearly on the volume of the external tank in which the hydrogen is delivered.

Experimental behaviour of a three-stage metal hydride hydrogen compressor

“…The P-c-I curves displayed in Figure 3 match with those of the alloys studied in previous works for a simulation and design of a three-stage MHHC system [15]. An important feature observed in Figures 3 a b and c is the very large thermal drifts for all alloys due to the use of a large alloy mass.…”

“…The need for more than one cycle to fully charge the last stage results from the fact that same alloy mass is used in each stage. According to previous works [15], these masses should have a ratio approximately of 1:2:3 for stages 1, 2 and 3, respectively, to compress hydrogen in one cycle. The operation and behavior of the three stage MHHC measurement system, (b) followed path in the absorption P-c-I´s at TL = 23ºC.…”

“…For the final assembly of the MHHC, the materials selected were the same AB2 alloys used in previous works [15] (a low B1, a medium B2 and a high B3 plateau pressure hydride, Table 1) but synthesized in larger quantities (≈100 g in total for each type) by induction melting. Morphological and microstructural characterisation of these alloys are described in ref [15]. The samples used in the present investigation were shortly milled, sieved with particle size between 150 µm and 1.2 mm and poured in the reactors (Figure 2.…”

Techno-Economic Analysis of High-Pressure Metal Hydride Compression Systems

“…However, the system is comprised of six-stage metal hydride compressors, using AB 5 and AB 2 materials. Galvis et al [7] also analyze the use of a three-stage MH compressor, comprised of AB 2 -type materials (Ti-Zr-Cr-Mn-V), to achieve an overall compression ratio of about 82. The system was designed to reach a pressure of 115 bar, with inlet pressure of 1.4 bar and a maximum desorption temperature of 100 • C. None of the proposed systems were designed for pressures on the order of 875 bar, as required by the DOE targets, and consequently, the techno-economic feasibility of systems achieving very high pressures was never examined.…”

Thermodynamic features of metal hydride thermal sorption compressors and perspectives of their application in hydrogen liquefaction systems

“…This feature forms a basis of thermo-chemical technology of hydrogen compression realised in a thermal sorption compressor (TSC) utilising metal hydrides (MHs), in which exothermic and endothermic processes of H 2 absorption and desorption in the MH are similar to processes of suction and discharge in a mechanical compressor [1,[6][7][8][9][10][11][12][13]. As a rule, the development of an MH TSC is preceded by its modelling aimed at the determination of the number of H 2 compression stages including proper selection of the MH materials to provide compression from p 1 = p min to p 2 = p max (specified by a customer) over an available temperature range, T 1 = T min … T 2 = T max [13][14][15][16], as well as optimisation of heat transfer performance in the MH beds in MH containers for hydrogen compression (generators-sorbers) to improve the dynamic characteristics of the TSC [14,[16][17][18].…”