Optimal absorbents of CO2 hydrate formation and energy consumption analysis for district cooling application under low pressure conditions

Abstract

Hydrate-based CO2 capture technology is considered one of the most applicable methods for carbon capture, utilization, and storage, owing to its vast potential and cost effectiveness. Hydrate slurries with an appropriate solid fraction guarantee applicable flowing conditions, and their high dissociation enthalpy permits their use for cold thermal energy transportation. Nevertheless, the required conditions for hydrate formation make the direct capture and subsequent utilization of hydrate slurries challenging. Thus, thermodynamic promoters have been introduced to the hydrates to alleviate the formation conditions and facilitate their practical application. Tetrahydrofuran and tetra-n-butylammonium bromide are selected because of their inherent interaction with water molecules during hydrate formation. Hydrate formation using the pure promoters as well as a mixture of the two is evaluated based on various perspectives. The induction time, hydrate growth period, CO2 capture ratio, and exothermic behavior of each absorbent are assessed under varying concentration and formation conditions. These key parameters provide considerable insight for determining optimal conditions for hydrate slurry-based cold thermal transportation. Based on the performance evaluation, three cases of single promoters and three mixed promoters under the condition of 3 bar are selected for the measurement of dissociation enthalpy. The results reveal that under 3 bar formation conditions, a 3:1 (THF mol%: TBAB mol%) concentration is suitable for ensuring a sufficiently high heat of dissociation and rapid hydrate slurry formation to permit considerable CO2 capture. Consequently, an alternative to a conventional district cooling system by replacing it with a CO2 hydrate slurry cooling system is proposed, and a sufficient reduction in energy consumption is demonstrated.