LNG cold energy recovery for salmon aquaculture

Conventional LNG regasification involves direct heat exchange between the LNG and sea water or other heat sources, meaning that the cold energy is wasted alongside the large mechanical power required to drive the seawater pumps. The global potential for cold production from LNG has been estimated at nearly 12 GW. This "cold energy" could be reused in a variety of processes such as power generation, air separation, traditional desalination, cryogenic carbon dioxide capture, etc. ^[1]

Besides, when conventional LNG vaporisers release cold energy into sea water, the environment and the ecosystem nearby LNG receiving terminals are affected. Therefore, utilisation of the cold energy from LNG re-gasification process has three advantages: (1) a useful utilisation of cold energy itself, (2) a saving in energy consumption during re-gasification process, and (3) an improvement in environmental problem caused by cold energy release. ^[2] 

According to a recent study, LNG cold energy can create new high-value industries, such as land-based aquaculture. ^[3] Atlantic salmon (Salmo salar), one of the major species produced in world aquaculture, is known to survive only at temperatures below 17 °C–19 °C. To breed Atlantic salmon in areas where the seawater temperature can sometimes exceed 17 °C–19 °C, cold seawater must be supplied or generated. Countries where Atlantic salmon is highly demanded but cannot be bred in conventional aquaculture methods (such as South Korea) are almost entirely dependent on imports.

As one of the top three importers of LNG worldwide, South Korea possesses a significant amount of available LNG cold energy (2645 MW), and all LNG receiving terminals in the country are in the coastal region. ^[3] In a recent study, a team of researchers in Korea proposed a new concept of land-based Atlantic salmon farming utilising cold energy from liquefied natural gas (LNG). ^[3] Due to limitations such as the safety of the laboratories as well as the physical scale of the LNG supply process, liquid nitrogen was used as a cold energy source to replace LNG in this experiment. The researchers conducted their laboratory-scale experiments to confirm whether the water temperature in a fish farming tank can fall below 17°C within an hour.  

Based on their experimental results and considering the LNG supply mass flow rate of 220.5 kg/s at the Tongyeong LNG receiving terminal, as well as the actual tank size for Atlantic salmon farming, the researchers found an estimated production capacity of approximately 14,000 tons. This is equivalent to 36.8% of the salmon imports to South Korea in 2019. In order to introduce this concept into the land-based aquaculture industry, further studies will be needed, namely to conduct economic analysis and optimising farming conditions on a real scale. 

Sources 

[1] Baha M., Dupont J. L., Bauer H. IIR (2022). Liquefied Natural Gas: production process and cold energy recovery. https://iifiir.org/en/encyclopedia-of-refrigeration/liquefied-natural-gas-production-process-and-cold-energy-recovery-br-nbsp  

[2] Sung, T., Kim, K.C. (2017). LNG Cold Energy Utilization Technology. In: Zhang, X., Dincer, I. (eds) Energy Solutions to Combat Global Warming. Lecture Notes in Energy, vol 33. Springer, Cham. https://doi.org/10.1007/978-3-319-26950-4_3  

[3] Baek, S.; Choi, W.; Kim, G.; Seo, J.; Lee, S.; Jeong, H.; Sung, Y. Liquefied Natural Gas Cold Energy Utilization for Land-Based Cold Water Fish Aquaculture in South Korea. Energies 2022, 15, 7322. https://doi.org/10.3390/en15197322