Ammonia as a hydrogen carrier: Engineering liquid-phase storage in underground salt caverns

Abstract

Ammonia (NH 3 ) provides a complete energy value chain, but its large-scale use is constrained by the absence of a viable grid-scale storage method. This study shows that intermittent renewable production and the diverse purity demand of end-use technologies make long-duration, high-capacity storage a technical requirement. The results suggest that salt caverns are the most suitable geological candidate capable of meeting this requirement. Our quantitative analysis indicates that liquid ammonia storage in salt caverns provides more than 300 times the energy capacity of gaseous ammonia storage in the same volume. This study provides a technical evaluation of operational envelope from an integrated thermodynamic and geochemical analysis. It confirms that stable liquid storage is achievable only in deep caverns, typically deeper than 500 m. We then quantify the key engineering challenges that must be addressed for practical deployment: (i) a one-time loss of ammonia due to its dissolution into the brine sump. It also creates a large volume of highly alkaline, corrosive fluid that complicates decommissioning; (ii) the requirement for an inert, immiscible compensating fluid to displace liquid ammonia during injection and withdrawal; and (iii) the reactions between ammonia and specific minerals present in the host formation. Ultimately, these integrated findings establish a focused research roadmap that addresses the remaining barriers and supports the use of ammonia as a large-scale hydrogen carrier.