A method of cooling a boil-off gas (BOG) stream from a liquefied gas tank comprising at least the step of heat exchanging the BOG stream with a first refrigerant in a heat exchanger, the heat exchanger having an entry port and a warmer exit port, and comprising at least the steps of: (a) passing the first refrigerant into the entry port of the heat exchanger and into a first zone of the heat exchanger to exchange heat with the BOG stream, to provide a first warmer refrigerant stream; (b) withdrawing the first warmer refrigerant stream from the heat exchanger at an intermediate exit port between the entry port and the warmer exit port; (c) admixing the first warmer refrigerant stream with an oil-containing refrigerant stream to provide a combined refrigerant stream; (d) passing the combined refrigerant stream into the heat exchanger through an entry port located in a second zone of the heat exchanger that is warmer than the first zone; (e) passing the combined refrigerant stream out of the heat exchanger through the warmer exit port. The present invention is a modification of a refrigerant cycle for BOG cooling, and LNG re-liquefaction in particular, that allows the use of a cost-efficient oil-injected screw compressor in the refrigerant system. The present invention is also able to accommodate the possibility of different flows or flow rates of the first refrigerant stream and the oil-containing refrigerant stream, such that there is reduced or no concern by the user of the process in relation to possible oil freezing and clogging of the heat exchanger caused by variation of the flow or flow rate of the oil-containing refrigerant stream.

Provided is a method of constructing a natural gas liquefaction plant, which can shorten a construction time period by minimizing effect of a lead time for the refrigerant compressor thereon, the method including: transporting a refrigerant compression module body 175 to an installation area 85, wherein the refrigerant compression module body is provided with a frame 120 configured to allow refrigerant compressor 150 for compressing a refrigerant for cooling natural gas to be mounted therein; installing the refrigerant compression module body 175 to the installation area 85; and mounting the refrigerant compressor 150 into a mounting space 130 predefined in the frame 120 of the installed refrigerant compression module body.

Provided is a cooling device with which it is possible to cool a fluid to be cooled, even before maintenance work, if a fault such as a blockage or a breakage occurs in a part of a channel. The cooling device (1) is provided with four heat exchangers (1A-1D) and a plurality of heat exchanger connection parts (111-120), each of the heat exchanger connection parts allowing natural gas to flow therethrough. Each of the heat exchangers has: a drum (101, 102, 103, fourth drum 104), a refrigerant reservoir (T), a plurality of heat exchanger core parts (121, 122, 123, 124) immersed in liquid propane in the refrigerant reservoir (T), and a demister (106). A plurality of cooling channels allowing natural gas to flow therethrough are installed, independent of each other, from the first heat exchanger (1A) to the fourth heat exchanger (1D).

The disclosure provides a method and system for optimizing production of a natural gas liquefaction process, the method comprising the steps of: selecting at least one manipulated variable (MV) for controlling the liquefaction process; selecting at least one control variable (CV), the at least one control variable at least comprising liquefied natural gas (LNG) throughput; providing at least one model, each model providing a dependency of the at least one control variable (CV) on the at least one manipulated variable (MV); using the at least one model to estimate LNG throughput for at least one of the manipulated variables (MV); obtaining process data from the liquefaction process, the process data at least including observed values of LNG throughput; creating a gain matrix based on said interdependencies; and using the gain matrix to optimize a process control system of the liquefaction process.

A method for determining an operating condition of a liquefied natural gas plant (2) includes preparing a training model (88) generated by machine learning using training data in which operating conditions data including a composition of a feed gas, a composition of a mixed refrigerant, and an ambient temperature and operation result data including a production efficiency of a liquefied product containing liquefied natural gas and a heavy component of the feed gas are associated together; and determining, as one new operating condition, a composition of the mixed refrigerant that optimizes a production efficiency of the liquefied natural gas predicted by the training model (88) from a latest composition of the feed gas in the liquefied natural gas plant (2) and a latest ambient temperature.

An equipment safety management device for managing safety of equipment capable of holding fluid is provided. The equipment safety management device includes: a safety means configured to be in fluid communication with an outlet of the equipment, the safety means being brought into a released state when pressure of the equipment reaches a previously set pressure, the safety means delivering the fluid to a flare pipe, which is fluidly communicated; and, as the flare pipe, at least one first flare pipe allowing a low-temperature fluid to flow therethrough and at least one second flare pipe allowing an aqueous fluid to flow therethrough. The safety means can deliver the fluid to both the first flare pipe and the second flare pipe.

A system and method for liquefaction of a natural gas stream utilizing a plurality of asymmetric parallel pre-cooling circuits. The use of asymmetric parallel cooling circuits allows for greater control over each refrigerant stream during the cooling process and simplifies process control by dedicating heat exchangers to performing similar duties.

A LNG liquefaction plant includes a propane recovery unit including an inlet for a feed gas, a first outlet for a LPG, and a second outlet for an ethane-rich feed gas, an ethane recovery unit including an inlet coupled to the second outlet for the ethane-rich feed gas, a first outlet for an ethane liquid, and a second outlet for a methane-rich feed gas, and a LNG liquefaction unit including an inlet coupled to the second outlet for the methane-rich feed gas, a refrigerant to cool the methane-rich feed gas, and an outlet for a LNG. The LNG plant may also include a stripper, an absorber, and a separator configured to separate the feed gas into a stripper liquid and an absorber vapor. The stripper liquid can be converted to an overhead stream used as a reflux stream to the absorber.

A system and method for integrated heavy hydrocarbon removal in a liquefaction system having a lean natural gas source. An economizer located between a main cryogenic heat exchanger and a reflux drum is provided to cool an overhead vapor stream against a partially condensed stream. In addition, pressure of the natural gas feed stream is maintained into a scrub column. A pressure drop is provided by a valve located between the economizer and the reflux drum on a partially condensed stream withdrawn from the cold end of the warm section of the main cryogenic heat exchanger.

A natural gas liquefaction system includes a piping rack for supporting a raw material gas transporting pipe for transporting the raw material gas; a pre-cooling heat exchanger for pre-cooling the raw material gas with a first refrigerant; a first refrigerant compressor for compressing the first refrigerant; a plurality of first air-cooled heat exchangers disposed on a top of the piping; a liquefier for liquefying the raw material gas which has been cooled by the pre-cooling heat exchanger, wherein the piping rack has a widened section along a part of a length of the piping rack, wherein the pre-cooling heat exchanger and the first refrigerant compressor are disposed on either side of the widened section of the piping rack, and are connected to each other via a first refrigerant transporting pipe extending in a direction intersecting a lengthwise direction of the piping rack for transporting the first refrigerant.