(746a) The State of the Art Prototype Design for Clathrate Hydrate Based Desalination (HyDesal) Process Utilizing LNG Cold Energy

The state of the art prototype design
for clathrate hydrate based desalination (HyDesal) process utilizing LNG Cold
Energy

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

Desalination is one of the most
promising technologies to mitigate an emerging water crisis. Thermal
desalination and reverse osmosis are two of the most widely employed
desalination technologies in the world. However, these technologies are energy
intensive. In countries like Singapore which lack natural water and energy
resources, it is imperative to develop innovative energy-efficient technologies to strengthen the energy-water nexus. Clathrate hydrate based
desalination (HyDesal) is one such technology. 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
the HyDesal process was proposed almost 70
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 reported an enhanced hydrate formation
kinetics in fixed bed reactor with silica sand as porous media when the hydrate is formed from a gas mixture consisting propane as co-guest.
Based on the ability of propane to draw dispersed water from the sand bed towards the gas phase for hydrate
growth, we proposed a conceptual hydrate based desalination (ColdEn-HyDesal) process employing fixed bed reactor
configuration 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 to address the
slow kinetics and effective separation of the hydrate crystals.¹ In this presentation, our state of the
art prototype design and optimized process conditions will be presented. An
optimal heat exchanger network for the ColdEn-HyDesal
process is obtained by employing mathematical programming based heat
integration methodology. By utilizing the waste LNG cold energy to produce
water, the energy consumption of ColdEn-HyDesal can
be reduced significantly making it a sustainable approach to strengthen the energy-water nexus.²

With our innovative reactor design,
we carried out water recovery experiments to find the suitable guest gas
mixture containing propane as co-guest. The other constituent in
the gas mixture employed were methane, argon, nitrogen and carbon dioxide.
Further kinetic experiments were carried out to optimize the silica sand
particle size, bed height. Our recent knowledge on enhancing the kinetics of
hydrate formation and innovative approach to offset the refrigeration cost for
the HyDesal process can be applied to efficiently desalinate seawater to
produce potable water. With our innovative reactor design and utilizing waste
LNG cold energy, HyDesal can be a sustainable solution for desalination.³ The ColdEn-HyDesal
process utilizing waste LNG cold energy will have a huge impact globally as
well due to the expanding number of LNG terminals and the potential to mitigate
the potable water issues.

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.

3.         Linga P, Babu P, Nambiar A. Novel
Reactor Designs and Method to Apply the Clathrate Hydrate Based Desalination
Utilizing LNG Cold Energy. PCT Filing
No.: PCT/SG2018/050083.