The state of the art prototype design and optimized process conditions for clathrate hydrate based desalination HyDesal process

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 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 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 hydrate is formed from gas mixture consisting propane as co-guest. Based on the ability of propane to draw dispersed water from 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. 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. In this presentation, our state of the art prototype design and optimized process conditions will be presented. 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. The ColeEn-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.