3128 -- Design Considerations for Fixed-Bed Metal Hydride Heat Pumps for High-Temperature Boosts PDF

Hydride alloy requirements for industrial size heat pumps (8.8 x 10⁶ W) to achieve temperature amplification of up tp 260°C or better, is investigated on the basis of the mass transfer zone concept of absorption bed design, cost of energy at 0.474¢/10⁶ J, and a return on capital investment of two years.

The Van’t Hoff curves for various metals in the temperature and pressure ranges of interest were found in the literature. Design equations pertaining to overall material and heat balances are presented. The computed results show that even under the idealized conditions of no resistance to mass transfer (stoichiometric wave front), absence of hysteresis, resilience to poisoning, alloy stability, constant absorption capacity, and alloy durability for two years, the estimated alloy required per bed would be between 15,872 - 22,675 kg, depending on the particular alloys chosen. Based on alloy costs of $33/kg and cost of energy at 0.474¢/10⁶ J, the allowable metal in each bed for a two-year payback works out to be 4535 kg. The actual alloy requirements are, therefore, four to five times greater than what process industries are willing to accept.

Units: SI