Liquefied natural gas (LNG) and DC electric power transfer system by cryogenic pipe of superconducting DC power transmission (SCDC)

Abstract We propose a hybrid energy transmission pipeline that combines the liquefied natural gas (LNG) cryogenic pipelines and superconducting direct current (DC) electrical power transmission cable system (SCDC). The system design is based on experimental data from the SCDC Ishikari project in Japan and related laboratory experiments. The particular structure of the hybrid cryogenic pipe connects the thermal radiation shield of the pipe that contains the DC high temperature superconducting (HTS) electrical cable to the LNG pipe and significantly reduces the heat leak into the SCDC pipe. Because the specific heat of LNG is higher than that of liquid nitrogen and the LNG transfer rate is quite high, the thermal loss of the SCDC cable becomes only 1/100 that of present-day conventional copper cables, far below the factor 1/10 reduction achievable by a stand-alone SCDC transmission lines. The LNG temperature rises by less than 2 K over a 100 km transport distance, which is negligible in actual use. LNG also saves significantly on pumping power compared to a natural gas pipeline. To liquefy the LNG at cryogenic temperature from natural gas at ambient temperature requires a large refrigerator that consumes enormous power. The gas pipeline, however, needs a compressor to produce high-pressure gas, which also consumes a massive amount of power. Due to these considerations, the proposed hybrid system is a viable design for the long-distance joint transportation of LNG and electricity.