A novel conceptual design of hydrate based desalination (HyDesal) process by utilizing LNG cold energy

Liquefied Natural Gas (LNG) is the best mode to transport natural gas from producing locations to importing countries when pipeline transport is not feasible. LNG industry has seen a phenomenal growth due to the widespread adoption of natural gas as a clean fuel. There is an ongoing effort to develop new technologies that can utilize LNG cold energy which is mostly being wasted at the LNG regasification terminals around the world. This work presents a novel conceptual design for a clathrate hydrate based desalination (HyDesal) process by utilizing LNG cold energy (ColdEn-HyDesal). This ColdEn-HyDesal process overcomes the high energy consumption of the traditional HyDesal process by using the cold energy of LNG to replace the external refrigeration cycle. An optimal heat exchanger network for the ColdEn-HyDesal process is obtained by employing mathematical programming based heat integration methodology for the LNG flow rate of 1000 kg/h in an LNG regasification terminal. The results indicate that the specific energy consumption (SEC) of the HyDesal process is 65.29 kWh/m3 of potable water, while that of the ColdEn-HyDesal process is only 0.60 kWh/m3 when the hydrate former is not recycled. When the hydrate former is recycled, then the specific energy consumption of the HyDesal process is 65.13 kWh/m3, while that of the ColdEn-HyDesal process is only 0.84 kWh/m3. In addition, the effects of recovery pressure, water recovery rate, and NaCl concentration in seawater on SEC and the volumetric rate of potable water are also analyzed and discussed. The results show that the SEC decreases substantially (27.42%) with the increase of water recovery from 40% to 70% in one hour. Further, the NaCl concentration in the feed has a small impact on the SEC, which only increases by 2.81% when the NaCl concentration increases from 3.5 wt% to 7.0 wt%. Thus, the ColdEn-HyDesal process is an energy efficient desalination process and can be a potential technology to desalinate seawater, and high concentration brines in an LNG regasification terminal.