Hydrogen Storage Using Slurries of Chemical Hydrides

Abstract

The usual storage technologies considered for hydrogen are compressed hydrogen, liquid hydrogen, metal hydrides, and carbon-based storage systems. Over the past couple of years another method of hydrogen storage and transmission has been under investigation that offers some significant advantages over the usual hydrogen storage technologies. Thermo Power Corporation has been developing a chemical hydride slurry approach. In this approach, a light metal hydride is used as the hydrogen carrier and storage media. Light metal hydrides such as lithium hydride, magnesium hydride, sodium hydride, and calcium hydride produce hydrogen when they react with water. These materials are typically dry solids at ambient conditions. The oil in the slurry protects the hydride from unintentional contact with moisture in the air and makes the hydride pumpable. At the point of storage and use, a chemical hydride/water reaction is used to produce high-purity hydrogen. An essential feature of this approach is the recovery and recycle of the spent hydride at centralized processing plants to produce new hydride slurry, resulting in an overall low cost for hydrogen. This chemical hydride slurry system has several benefits: it greatly improves the energy transmission and storage characteristics of hydrogen as a fuel, it provides a hydrogen storage medium that is stable at normal environmental temperatures and pressures, it is pumpable and easily transported, it has a high gravimetric and volumetric energy density, with the use of a properly designed reactor it can provide hydrogen at elevated pressures without the use of a compressor, it produces the hydrogen carrier efficiently and economically from a low cost carbon source, and since the production of the hydride is a carbo-thermal process performed at a centralized plant, CO2 resulting from the carbo-thermal process for refining lithium is concentrated and amenable to sequestration.