Method and apparatus for reliquefying and returning boil-off gas (BOG) to a liquefied natural gas (LNG) tank, the method including: Withdrawing BOG (F2) from the headspace of an LNG tank; compressing the BOG in a first compression stage to a first pressure p.sub.1 between 8 and 18 bara and tapping of a first portion of this gas; further compressing a second portion of the gas from step in a final compression stage to a second pressure p.sub.2?120 bara; cooling at least part of the further compressed gas to a first temperature T.sub.1 between ?20? C. and ?100? C.; expanding the gas from step to a third pressure p.sub.3 between 8 and 20 bara; and separating the gas from step into a liquid phase and a gaseous phase to combine the gaseous phase with the tapped first portion of the gas from the first compression stage and to return the liquid phase into the LNG tank.

Provided is a partial reliquefaction system including a boil-off gas (BOG) compression system receiving a BOG exiting from a liquefied natural gas (LNG) storage tank, a high-pressure compression section receiving a BOG stream from the BOG compression system, a heat exchanger effectuating a temperature drop of the BOG stream, an expander receiving the cooled BOG stream after passing through the heat exchanger, and a separator vessel for receiving a gas/liquid mixture, wherein a gas portion of the gas/liquid mixture is recirculated through the heat exchanger to act as the cooling medium for the heat exchanger.

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 ship comprises an engine; a first self-heat exchanger which heat-exchanges boil-off gas discharged from a storage tank; a multi-stage compressor which compresses, in multi-stages, the boil-off gas that passed through the first self-heat exchanger after being discharged from the storage tank; a first decompressing device which expands one portion of the boil-off gas compressed by the multi-stage compressor; a second self-heat exchanger which heat-exchanges the other portion of the boil-off gas compressed by the multi-stage compressor, with the boil-off gas expanded by the first decompressing device; and a second decompressing device which expands the boil-off gas pre-cooled by the second self-heat exchanger and cooled by the first self-heat exchanger, wherein the first self-heat exchanger uses the boil-off gas discharged from the storage tank as a refrigerant for cooling the boil-off gas that passed through the second self-heat exchanger after being compressed by the multi-stage compressor.

A refrigerant charging system includes: a reliquefaction system reliquefying boil-off gas generated in a liquefied gas storage tank by compressing the boil-off gas and subjecting the compressed boil-off gas to heat exchange with refrigerant supplied to a heat exchanger while circulating along a refrigerant circulation line; a buffer tank storing utility N.sub.2 to be supplied to the ship; a booster compressor receiving the utility N.sub.2 from the buffer tank, compressing the received N.sub.2, and supplying the compressed N.sub.2 to the refrigerant circulation line; and a first load-up line along which the N.sub.2 is supplied from the buffer tank to the refrigerant circulation line without passing through the booster compressor. Upon initial charging in a non-operation state of the reliquefaction system, the refrigerant circulation line is charged with refrigerant by supplying the N.sub.2 from by a pressure differential between the refrigerant circulation line and the buffer tank.

A method for condensing argon can include two flow streams interacting with each other in a heat exchanger found within a cold box: a stream of gaseous argon enters the heat exchanger to be cooled down below its liquefaction point by a stream of pressurized liquid nitrogen entering the heat exchanger. While passing through the heat exchanger, gaseous argon is gradually cooled down until it is condensed into liquid, flowing by gravity to the nearby liquid argon storage tank.

An apparatus for condensing argon can include cold box, which is preferably sealed and largely maintenance free, where all instruments and valves requiring routine maintenance are to be located outside, a nitrogen separator disposed within the cold box, a heat exchanger disposed within the cold box, the heat exchanger is configured to condense a gaseous argon stream against a pressurized liquid nitrogen stream. The cold box is elevated as compared to an argon storage vessel, such that the condensed argon stream can flow to the argon storage vessel without the need for a pump.

Systems and methods for controlling the temperature and pressure of a cryogenic liquid methane storage unit are provided. The disclosed systems and methods generate methane gas from a reservoir of liquid methane stored within the methane storage unit, vent the methane gas through one or more outlet valves connected to the methane storage unit, and generate electric power using the vented methane gas. The generated electric power can then be used to initiating a cooling cycle, which reduces the temperature of said reservoir of liquid methane and reduces the pressure in said methane storage unit. Micro anaerobic digesters and methane storage units may be configured in a networked environment with a central controller that monitors remote units.

Systems and methods for controlling the temperature and pressure of a cryogenic liquid methane storage unit are provided. The disclosed systems and methods generate methane gas from a reservoir of liquid methane stored within the methane storage unit, vent the methane gas through one or more outlet valves connected to the methane storage unit, and generate electric power using the vented methane gas. The generated electric power can then be used to initiating a cooling cycle, which reduces the temperature of said reservoir of liquid methane and reduces the pressure in said methane storage unit. Micro anaerobic digesters and methane storage units may be configured in a networked environment with a central controller that monitors remote units.

The present invention is to provide a BOG processing apparatus. The BOG processing apparatus includes a cooling device, a second cooling device, and a recovery device. The cooling device has a cooling drum, a BOC inlet part introducing the BOG, a first spray spraying LNG in an upward direction, a first filled layer contacting with the LNG and the BOG, a second spray spraying the LNG in a downward direction, a third spray spraying the LNG in a downward direction, a second filled layer adsorbing mist in the BOG, and a mist eliminator eliminating the mist in the BOG.