Power cycles based upon cyclical hydriding and dehydriding of a material

A method for deriving power from a low-grade thermal energy source and a relatively higher-grade thermal energy source comprising:

• combining hydrogen gas with a hydride-forming material under conditions of temperature and pressure such that a hydride saturated with, and in equilibrium with, hydrogen gas is formed;
• using a relatively low-grade thermal energy source at a temperature, T.sub.1, to heat the hydride at constant volume to a temperature above the equilibrium temperature of the hydride to activate the hydride by chemically compressing the hydrogen gas;
• transferring heat to the activated hydride from said low-grade thermal energy source, and concurrently releasing the hydrogen gas therefrom at elevated pressure;
• conveying the released hydrogen gas from the hydride to a first power producing expansion device;
• expanding the hydrogen gas through said first power producing expansion device to a pressure above the equilibrium pressure of said hydride-forming material to produce power and cool the hydrogen gas to a temperature T.sub.2 ;
• passing at least a portion of the cooled hydrogen gas from said first power producing expansion device, after expansion therethrough, into heat exchange relation to a relatively higher-grade thermal energy source at a temperature T.sub.3 which is higher than temperature T.sub.2 to heat the hydrogen gas from said expansion device;
• and
• conveying the heated hydrogen gas, following heat exchange with said relatively higher-grade thermal energy source, to a second power producing expansion device;
• expanding the hydrogen gas conveyed to said second power producing expansion device through said second power producing expansion device to produce power and cool the hydrogen gas to a temperature at least as low as the temperature T.sub.1 at which said hydride is saturated with, and in equilibrium with, hydrogen gas;
• and
• recycling the hydrogen gas after expansion through said second power producing expansion device to said hydride-forming material;
• and
• cyclically repeating the foregoing steps.