(746e) Stability Assessment of Hydrate Pellets for Energy Storage

Stability
assessment of hydrate pellets for energy storage

Hari Prakash Veluswamy^{^},
Asheesh Kumar and Praveen Linga*

Abstract

Widespread applications
of natural gas (NG) and the increasing global demand of the cleanest burning
fossil fuel necessitate effective and efficient methods for natural gas storage
/transportation. Storing natural gas in hydrates via SNG (solidified natural
gas) is highly advantageous due to several advantages that include possessing high
volumetric capacity, offering high degree of safety owing to non-explosive
nature and being relatively less energy intensive compared to conventional
methods of NG storage¹.It is envisaged to store hydrates
in the form of pellets to enable the ease of handling during transport and long-term
storage. In addition to prevailing challenges during the hydrate formation
(prolonged induction time and sluggish kinetics), there are a few challenges
from the storage perspective as well.

Relatively
less understood ‘self-preservation’ plays a key role in enabling the storage of
sI hydrate pellets at 253.2 K (about 60 degrees higher than equilibrium temperature
of 193 K at 1 atm). sI hydrates are thermodynamically unstable but kinetically
stable in these conditions due to the formation of ice shell around the
pellets. Though few studies have demonstrated the prolonged storage of hydrate
pellets at 253 K relying on the anomalous self-preservation², it has
to be noted that this process is energy intensive requiring significant cost
for large scale and long-term storage applications. Mixed methane or natural
gas hydrates formed in presence of thermodynamic promoters like THF
(tetrahydrofuran) offer a viable solution to this problem enabling the hydrate
pellets to be stored at comparatively high temperatures of about 268.2 – 273.2
K at atmospheric pressure albeit a slight offset in storage capacity due to the
presence of thermodynamic promoter in the hydrates. These mixed hydrate pellets
are thermodynamically stable and do not rely on the self-preservation effect,
making them highly suited for commercial deployment.

In this
study, we evaluate the stability of hydrate pellets of sI and sII structures with
similar dimensions synthesized from hydrates formed from water and different starting
solutions at chosen experimental conditions. All hydrate pellets were stored in
individual vessels with pressure and temperature monitoring at constant
temperatures under atmospheric pressure for several months. The current study
provides salient information on the stability of different hydrate structures
and investigates the role of ‘self-preservation’ in hydrate pellet stability of
different hydrate structures at chosen temperatures.

Keywords: energy
storage; clathrate hydrates; hydrate pellets; natural gas; stability

¹ H. P. Veluswamy,
A. Kumar, Y. Seo, J. D. Lee and P. Linga, Applied Energy, 2018, 216, 262-285.

²
H.
Mimachi, M. Takahashi, S. Takeya, Y. Gotoh, A. Yoneyama, K. Hyodo, T. Takeda
and T. Murayama, Energy & Fuels, 2015, 29, 4827-4834.

^{^}presenting author: Tel:
(65) 6601-4913; e-mail: chehpv@nus.edu.sg

*corresponding
author: Tel: (65) 6601-1487; e-mail: chepl@nus.edu.sg