Integrated Aluminum-Water Technology for Hydrogen Production

In this paper, the features of the hydrothermal oxidation of dispersed aluminum are outlined and the prospects of its use for the mass production of “carbon-free” hydrogen are substantiated. In the course of hydrothermal oxidation, aluminum reacts with water or steam. In this case, hydrogen without the admixture of carbon or its compounds and thermal energy are formed. The solid product of aluminum oxidation is represented by aluminum hydroxide. This paper describes an integrated low-waste aluminum-water technology using such a single consumable agent as electricity. The technology involves the reduction to the metal of the obtained aluminum hydroxide within the framework of a single production. The aluminum regenerated in the electrolysis process can be again returned to the cycle for obtaining hydrogen from water in the hydrothermal oxidation reaction. If relatively recently developed inert anodes, as well as electricity generated at hydroelectric power plants or nuclear power plants, are used in the electrolysis of aluminum, then the technology has no carbon traces. The weight-energy characteristics and the composition of the products of each of the main processes used in the integrated aluminum-water technology are analyzed, namely the reduction of aluminum from Al₂O₃ by means of electrolysis to return Al to the hydrogen-production cycle, the hydrothermal aluminum oxidation with the production of a steam-hydrogen mixture and a condensed mixture of water and boehmite, the obtaining of aluminum oxide Al₂O₃ from boehmite AlOOH, obtaining pure hydrogen from a steam-hydrogen mixture as well as water for reuse, and hydrogen compression. Serious attention is paid to the potentialities of utilizing the thermal energy of the steam-hydrogen mixture for hydrogen compression. Owing to the production low-grade heat in large amounts under implementing the technology of hydrothermal aluminum oxidation, a thermal sorption compressor can be used for compressing hydrogen to operating parameters (40–90 MPa). This makes it possible to reduce the operating costs for hydrogen compression by more than an order of magnitude compared to traditional mechanical compressors and, at the same time, to provide an increase in the efficiency of aluminum hydrothermal oxidation.