(746c) Evaluation of CO2/C3H8 Gas Mixture for Clathrate Hydrate Based Desalination (HyDesal) Process

Evaluation of CO₂/C₃H₈
gas mixture for clathrate hydrate based desalination (HyDesal) process

Ponnivalavan
Babu¹, Abhishek
Nambiar¹, Praveen Linga¹*

¹Department
of Chemical and Biomolecular Engineering, National University of Singapore, Singapore, Singapore 117 585

Keywords: gas
hydrates; desalination; clathrate process; seawater, cold energy, LNG

*corresponding
author: e-mail: praveen.linga@nus.edu.sg (P.
Linga); Tel: (65) 6601-1487; Fax: (65) 6779-1936.

Abstract

Clathrate
hydrate based desalination (HyDesal) process is based on a liquid to solid
phase change by employing a suitable guest gas/ gas mixture for the phase
change. In the HyDesal process, water molecules form cages around a guest
gas/liquid component effectively rejecting salts present in the brine solution
at temperatures slightly higher than the normal
freezing temperature of water. These crystals when dissociated or melted are
essentially fresh water and the guest component can be re-used for the process
again. While CHBD process was proposed almost 50 years ago, it was never
commercialized primarily due to the high energy requirement for low-temperature operation, slow hydrate
formation kinetics and inefficient hydrate crystal separation from brine.
Recently, we proposed a HyDesal process employing fixed bed reactor
configuration utilizing LNG cold energy to minimize the energy requirement.¹ The ability of propane as a co-guest to
draw water from the silica sand bed can be effectively used for the HyDesal
process addressing the slow kinetics and effective separation of the hydrate
crystals. By utilizing the waste LNG cold energy to produce water, the energy
consumption of HyDesal can be reduced significantly making it a sustainable
approach to strengthen the energy-water
nexus.²

In this study,
the effect of the CO₂/C₃H₈
gas mixture on water recovery is evaluated for desalination. Experiments
were carried out with pure water, 3 wt% NaCl solution and synthetic seawater in
a fixed bed reactor with sand as porous media to evaluate the kinetics of
hydrate formation, water recovery and salt rejection rate. The optimized
process conditions like propane concentration, bed height, silica sand particle
size and experimental pressure and
temperature were determined.

References

1.         Babu
P, Kumar R, Linga P. Unusual behavior of propane as a co-guest during hydrate
formation in silica sand: Potential application to seawater desalination and
carbon dioxide capture. Chemical
Engineering Science. 9/27/ 2014;117:342-351.

2.         He
T, Nair SK, Babu P, Linga P, Karimi IA. A Novel Conceptual Design of Hydrate
Based Desalination (HyDesal) Process by Utilizing LNG Cold Energy Applied Energy. 2018; In Press.