Zero emissions, low-energy water production system using clathrate hydrate: Engineering design and techno-economic assessment

Abstract

Seawater desalination via the crystallization using clathrate hydrate is a promising technology for displacing conventional desalination processes, yet the technology immaturity and poor cost performance are the issues to be resolved. In this study, conceptual designs of hydrate-based dual functional plant (desalination and salt production) utilizing the eutectic crystallization of hydrate and NaCl dihydrate have been presented on an industrial scale with the capacity of 24 m3/day. The conceptual design proposed in this study focuses on detailed and executive aspects, including the size of individual reactors, the selection of pumps, and the setting of operating temperature and pressure conditions. The process designs help meet these present demands on hydrate-based desalination and conform to the global standards of minimizing energy requirement and the disposal of environmental pollutants. Hydrate-based plant was designed as a novel Zero Liquid Discharge (ZLD) process to produce potable water and salt simultaneously, with the recovery ratio of pure water from seawater achieving 95%. The design-based cost estimation showed that the annual operating cost is estimated US$2.29/m3 for cyclopentane-hydrate-based plant and US$3.64/m3 for CO2-hydrate-based plant. The results suggest that the hydrate-based plants will bring gross profit comparable to the reported ZLD plants; that is, the gross profit will achieve US$20 per 1 m3 of water production. In addition to these two improvements over the existing plants, the hydrate-based process designs also exhibit favorable energy requirement compared to the eutectic system of ice. This design-based study may contribute to the promotion of additional construction of hydrate-based process unit to the existing reverse osmosis plant or even the new construction of hydrate-based desalination plant worldwide.