Liquefied gas treatment system for vessel

An LNG tank ship comprising:

• an LNG tank containing therein an LNG composition in liquid phase and gas phase;
• a gas fuel combustion device configured to consume gas phase LNG;
• a supercritical fuel injection engine configured to consume supercritical state LNG;
• a liquid discharge port located inside the LNG tank at a lower portion thereof and configured to discharge liquid phase LNG from the LNG tank;
• a gas discharge port located inside the LNG tank at a higher portion thereof and configured to discharge gas phase LNG from the LNG tank;
• a liquid-to-supercritical pathway for processing liquid phase LNG from the liquid discharge port to generate supercritical state LNG for supplying to the supercritical fuel injection engine, the liquid-to-supercritical pathway comprising a pump and a heater downstream of the pump;
• a gas-to-supercritical pathway for processing gas phase LNG from the gas discharge port to generate supercritical state LNG for supplying to the supercritical fuel injection engine, the gas-to-supercritical pathway comprising a gas phase LNG transfer line for receiving gas phase LNG from the gas discharge port, a heat exchanger downstream of the gas phase LNG transfer line, and a multi-stage compressor downstream of the heat exchanger;
• and
• a supercritical-to-liquid pathway for processing supercritical state LNG to generate liquid phase LNG for returning to the LNG tank, the supercritical-to-liquid pathway comprising a supercritical state LNG transfer line for receiving supercritical state LNG from the gas-to-supercritical pathway, the heat exchanger downstream of the supercritical state LNG transfer line, a decompressor downstream of the heat exchanger and a LNG return line downstream of the decompressor;
• wherein, in the liquid-to-supercritical pathway, the pump is configured to pressurize liquid phase LNG from the LNG tank to a pressure of 150-400 bara;
• wherein, in the liquid-to-supercritical pathway, the heater is configured to heat the pressurized liquid phase LNG for generating supercritical state LNG, wherein the heater is in fluid communication with the supercritical fuel injection engine for supplying at least part of the supercritical state LNG to the supercritical fuel injection engine;
• wherein the heat exchanger is configured to heat exchange between the gas phase LNG of the gas-to-supercritical pathway and the supercritical state LNG of the supercritical-to-liquid pathway such that the gas phase LNG of the gas-to-supercritical pathway is heated while the supercritical state LNG of the supercritical-to-liquid pathway is cooled sufficient to form liquid phase LNG, wherein the LNG tank ship does not comprise a refrigeration cycle of a coolant for cooling the supercritical state LNG in the supercritical-to-liquid pathway;
• wherein, in the gas-to-supercritical pathway, the multi-stage compressor comprises a plurality of serially connected compressors configured to pressurize the heated gas phase LNG for generating supercritical state LNG having a pressure of 150-400 bara, wherein the multi-stage compressor is in fluid communication with the supercritical fuel injection engine for supplying at least part of the supercritical state LNG from the multi-stage compressor to the supercritical fuel injection engine;
• wherein, in the supercritical-to-liquid pathway, the decompressor is configured to depressurize the liquid phase LNG from the heat exchanger;
• wherein, in the supercritical-to-liquid pathway, the LNG return line is in fluid communication with the LNG tank for returning the depressurized liquid phase LNG to the LNG tank,
• a valve system configured to control connection of the liquid-to-supercritical pathway to the liquid discharge port, connection of the gas-to-supercritical pathway to the gas discharge port, and connection of the supercritical-to-liquid pathway to the gas-to-supercritical pathway for selective operation of one or more of the liquid-to-supercritical pathway, the gas-to-supercritical pathway, and the supercritical-to-liquid pathway such that:
• the multi-stage compressor of the gas-to-supercritical pathway is not to operate for generating supercritical state LNG while the liquid-to-supercritical pathway is operating to generate supercritical state LNG, and
• the supercritical-to-liquid pathway is to operate only when the gas-to-supercritical pathway is operating to generate supercritical state LNG.