A ship comprises: a liquefied gas storage tank; a multi-stage compressor for compressing a boil-off gas discharged from a storage tank and comprising a plurality of compression cylinders; a second heat exchanger for heat exchanging a fluid, which has been compressed by the multi-stage compressor, and thus cooling same; a first decompressing device for expanding a flow (flow a1) partially branched from the flow (flow a) that has been cooled by the second heat exchanger; a third heat exchanger for heat exchanging, by flow a1 which has been expanded by the first decompressing device as a refrigerant, the remaining flow (flow a2) of flow a after excluding flow a1 that has been branched and thus cooling same; and a second decompressing device for expanding flow a2 which has been cooled by the third heat exchanger.

Disclosed is a re-liquefying device using a boil-off gas as a cooling fluid so as to reliquefy the boil-off gas generated from a liquefied gas storage tank provided in a ship. A boil-off gas re-liquefying device for a ship comprises: a multi-stage compression unit for compressing boil-off gas generated from a liquefied gas storage tank; a heat exchanger in which the boil-off gas generated from the storage tank and the boil-off gas compressed exchange heat; a vaporizer for heat exchanging the boil-off gas cooled by the heat exchanger and a separate liquefied gas supplied to a fuel demand source of a ship, and thus cooling the boil-off gas; an intermediate cooler for cooling the boil-off gas that has been cooled by the heat exchanger; and an expansion means for branching a part of the boil-off gas, which is supplied to the intermediate cooler, and expanding the same.

Disclosed herein is a BOG reliquefaction system for LNG vessels. The BOG reliquefaction system includes a compressor compressing BOG, a heat exchanger cooling the compressed BOG by exchanging heat between the compressed BOG and BOG used as a refrigerant, and an expansion unit for expanding the BOG having been cooled by the heat exchanger, wherein the heat exchanger includes a core, in which heat exchange between a hot fluid and a cold fluid occurs, the core including a plurality of diffusion blocks, and a fluid diffusion member diffusing a fluid introduced into the core or a fluid discharged from the core.

Disclosed is a re-liquefying device using a boil-off gas as a cooling fluid so as to re-liquefy the boil-off gas generated from a liquefied gas storage tank provided in a ship. A boil-off gas re-liquefying device for a ship comprises: a multi-stage compression unit for compressing boil-off gas generated from a liquefied gas storage tank; a heat exchanger in which the boil-off gas generated from the storage tank and the boil-off gas compressed exchange heat; a vaporizer for heat exchanging the boil-off gas cooled by the heat exchanger and a separate liquefied gas supplied to a fuel demand source of a ship, and thus cooling the boil-off gas; an intermediate cooler for cooling the boil-off gas that has been cooled by the heat exchanger; and an expansion means for branching a part of the boil-off gas, which is supplied to the intermediate cooler, and expanding the same.

A ship comprises: a tank; a multistage compressor for compressing a boil-off gas discharged from a storage tank and comprising a plurality of compression cylinders; a first heat exchanger for heat exchanging a fluid, which has been compressed by the multistage compressor, with the boil-off gas discharged from the storage tank and thus cooling the same; a first decompressing device for expanding a flow (flow a1) partially branched from the flow (flow a) that has been cooled by the first heat exchanger; a third heat exchanger for heat exchanging, by flow a1 which has been expanded by the first decompressing device as a refrigerant, the remaining flow (flow a2) of flow a after excluding flow a1 that has been branched and thus cooling the same; and a second decompressing device for expanding flow a2 which has been cooled by the third heat exchanger.

A ship comprises: a liquefied gas storage tank; a multi-stage compressor for compressing a boil-off gas discharged from a storage tank and comprising a plurality of compression cylinders; a second heat exchanger for heat exchanging a fluid, which has been compressed by the multi-stage compressor, and thus cooling same; a first decompressing device for expanding a flow (flow a1) partially branched from the flow (flow a) that has been cooled by the second heat exchanger; a third heat exchanger for heat exchanging, by flow a1 which has been expanded by the first decompressing device as a refrigerant, the remaining flow (flow a2) of flow a after excluding flow a1 that has been branched and thus cooling same; and a second decompressing device for expanding flow a2 which has been cooled by the third heat exchanger.

The system for treating a gas deriving from the evaporation of a cryogenic liquid and supplying pressurized gas to a gas engine according to the invention comprises, on the one hand, from upstream to downstream, a reliquefaction unit (10) with compression means (11, 12, 13), a first heat exchanger (17) and expansion means (30), and, on the other hand, a pressurized gas supply line comprising, from upstream to downstream, a pump (48) for pressurizing the liquid and high-pressure vaporization means (61).

The pressurized gas supply line has, upstream of the vaporization means (61), a bypass (57) for supplying a second heat exchanger (60) between, on the one hand, pressurized liquid of the supply line (56) and, on the other hand, a line (22) of the reliquefaction unit (10) downstream of the first exchanger and upstream of the expansion means (30).

Disclosed is a method of discharging lubricant oil from a BOG reliquefaction system configured to reliquefy BOG by compressing the BOG by a compressor, cooling the compressed BOG through heat exchange with non-compressed BOG by a heat exchanger, and reducing a pressure of fluid cooled through heat exchange by a pressure reducer. In the lubricant oil discharge method, the compressor comprises at least one oil-lubrication type cylinder and it is determined that it is time to discharge condensed or solidified lubricant oil, if at least one of preset conditions is satisfied.

A method for operating a heat exchanger, in which a first operating mode is carried out in first time periods, and a second operating mode is carried out in second time periods that alternate with the first time periods; in the first operating mode a first fluid flow is formed at a first temperature, is fed into the heat exchanger in a first region at the first temperature, and is partially or completely cooled in the heat exchanger; in the first operating mode a second fluid flow is formed at a second temperature, is fed into the heat exchanger in a second region at the second temperature, and is partially or completely heated in the heat exchanger; and in the second operating mode the feeding of the first fluid flow and of the second fluid flow into the heat exchanger is partially or completely halted.

The present invention relates to cryogenic energy storage systems for storing using high-grade heat-of-compression. The system includes a liquefaction sub-system (100) and thermal energy storage device (300). The liquefaction sub-system (100) includes a first compressor (102), a first, second and third heat exchanger (104, 116, 112) and second compressor (114). The first and second heat exchangers (104, 116) are configured to transfer the high-grade heat of compression from the first and second compressors (102, 114) respectively to the thermal energy storage device (300). The third heat exchanger (112) is configured to recuperate the low-grade heat of compression from the second compressor (114) back into the second compressor (114) enabling the second compressor (114) to generate high-grade heat of compression. Further systems use compressors (124) and expanders (122). Further systems include power recovery sub-systems (400). The present disclosure also relates to methods of heat-of-compression storage in cryogenic energy storage systems.