Metal Hydride Chemical Heat Pumps for Industrial Use

Abstract

Hydriding alloys are intermetallic absorbent compounds which have the remarkable quality of absorbing very large quantities of hydrogen gas per unit volume of metallic powder. The absorption and desorption of hydrogen are exothermic and endothermic reactions respectively, and take place according to a reversible chemical reaction. The temperatures at which these reactions occur depend upon the composition of the hydriding material and their preparation. These properties enable hydriding metals to be used in chemical heat pumps for upgrading industrial waste energy to supply useful energy in the form of process hot water or steam. With proper selection of the hydriding materials, temperature boosts of about 200 F can be obtained in a single stage cycle. This paper describes the state-of-the-art developments of metal hydride heat pumps (MHCHP). Details of the thermodynamic cycle, kinetics of hydriding reactions, physical construction limitations and potential areas of application are discussed.