Design of a Hydrogen Compressor Powered by Accumulated Heat and Generated in Metal Hydrides
Abstract
The proposed article describes a compressor design for using the heat generated in the hydrogen absorption process into the metal alloy during compression. The absorption of hydrogen into the alloy occurs after the desired pressure has been achieved, whereby the catalytic effect of the used metals to dissociate the hydrogen molecule and the subsequent diffusion of the hydrogen atoms into the intermetallic space of the lattice occur. The absorption process is accompanied by a gradual increase in pressure up to the total saturation value of the metal. The equilibrium pressure at which the absorption occurs is highly dependent on the temperature of the alloy. The difference in the equilibrium pressures of MH materials at an acceptable temperature change has led to efforts of creating a hydrogen compressor that would use MH heating and refrigeration heat cycle.
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Introduction
In nature hydrogen does not naturally occur in an unbound molecular form. It is most often produced through the partial oxidation of natural gas, steam reforming and electrolysis of water.
If it is not in use immediately after production, it is necessary to store it. Most storage methods, in view of the low hydrogen density, require the use of a compressor that increases the pressure to the desired level.
The hydrogen compressor is currently used to increase hydrogen pressure mainly through mechanical means. Rotary turbines are used at high volumetric flow rates, and at low flow rates there are mainly used piston compressors, or pressure multipliers utilizing hydraulic mechanisms. There was an attempt to test compressors using proton exchange membranes and simple compressors with metal hydride alloy.
The compressor powered by accumulated heat and generated in metal hydrides operates in a closed thermodynamic cycle, where hydrogen is stored at low temperatures with the catalytic effect of metals. Then the hydrogen molecules are dissociated and atomic diffusion into the intermetallic structure of the alloy occur. Once the alloy is saturated with hydrogen, it is necessary to bring in heat from an external source, thus increasing the pressure by shifting the working point to a higher isothermal curve. At higher temperatures, it is possible to desorb hydrogen from the alloy and reduce the storage capacity to the original state. It is possible to shift the subsequent lowering of the temperature to the starting point [1-4].
Conclusion
The article described the basic concept of the development of a hydrogen compressor using metal hydride materials with the tandem connection of tanks. A heat pump is designed for heat transfer, which minimizes the energy demand of hydrogen compression.
The development of a hydrogen compressor has great potential for innovative social and economic needs in the development and application of hydrogen technologies in the automotive industry and transport, mainly in the context of Slovak and European innovation strategy.
The economic benefit of the submitted work is limited by the implementation of the hydrogen economy, mainly in the automotive industry in Slovakia. The hydrogen compressor prototype is a unique solution in relation to safety of operation, since hydrogen does not come in contact with moving or compressing elements during compression or with the rotating parts of the system.