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 liquefaction system is capable of sequentially or simultaneously liquefying multiple feed streams of hydrocarbons having different normal bubble points with minimal flash. The liquefying heat exchanger has separate circuits for handling multiple feed streams. The feed stream with the lowest normal boiling point is sub-cooled sufficiently to suppress most of the flash. Feed streams with relatively high normal boiling points are cooled to substantially the same temperature, then blended with bypass streams to maintain each product near its normal bubble point. The system can also liquefy one stream at a time by using a dedicated circuit or by allocating the same feed to multiple circuits.

A process for liquefying a natural gas feed stream including cooling a feed gas stream to obtain a liquefied natural gas stream; introducing the liquefied natural gas stream into a deazotization column to produce a liquefied natural gas stream and a nitrogen-enriched vapor stream; at least partially condensing at least part of the nitrogen-enriched vapor stream to produce a two-phase stream; introducing the two-phase stream into a phase-separating vessel to produce a first liquid stream and a first nitrogen-enriched gas stream; introducing at least part of the nitrogen-enriched gas stream into a distillation column thereby producing a second nitrogen-enriched stream containing less than 1 mol % of methane and a second liquid stream containing less than 10 mol % of nitrogen; wherein at least part of the liquefied natural gas stream is used to cool the at least part of the nitrogen-enriched vapor stream in said heat exchanger.

Low-temperature refrigeration device arranged in a frame and comprising a working circuit forming a loop and containing a working fluid, the working circuit forming a cycle comprising in series: a compression mechanism, a cooling mechanism, an expansion mechanism and a heating mechanism, the device comprising a refrigeration heat exchanger intended to extract heat from at least one member by exchanging heat with the working fluid, the mechanisms for cooling and reheating the working fluid comprising a common heat exchanger in which the working fluid transits in counter-flow in two separate transit portions of the working circuit, the compression mechanism comprising at least two compressors and at least one motor for driving the compressors, the working fluid expansion mechanism comprising at least one rotary turbine, the device comprising at least one drive motor comprising a drive shaft, one end of which drives a compressor and the other end of which is coupled to a turbine, the motor being attached to the frame at at least one fixed point, the common heat exchanger being attached to the frame at at least one fixed point, the two counter-flow transit portions of the common heat exchanger being orientated in a longitudinal direction of the frame, the drive shaft of the drive motor being orientated in a direction parallel or substantially parallel to the longitudinal direction and the turbine and the compressor being arranged relatively longitudinally such that the turbine is located longitudinally on the side corresponding to the relatively cold end of the common heat exchanger when the device is being operated and the compressor is located longitudinally on the side corresponding to the relatively hot end of the common heat exchanger when the device is being operated.

Disclosed is a low-temperature refrigeration device which is arranged in a frame and comprises a working circuit that forms a loop and contains a working fluid, the working circuit forming a cycle comprising, connected in series: a compression mechanism, a cooling mechanism, an expansion mechanism and a heating mechanism, wherein the mechanisms for cooling and heating the working fluid comprise a common heat exchanger in which the working fluid flows in opposite directions in two separate transit portions of the working circuit, the device further comprising a refrigeration heat exchanger for extracting heat from at least one member by exchanging heat with the working fluid flowing in the working circuit, the compression mechanism comprising two separate compressors, the mechanism for cooling the working fluid comprising two cooling heat exchangers which are arranged respectively at the outlet of the two compressors and ensure heat exchange between the working fluid and a cooling fluid, wherein the frame extends in a longitudinal direction and comprises a lower base intended to be mounted on a support, the cooling heat exchangers are located in the frame about the common heat exchanger, i.e. the cooling heat exchangers are not located below the common heat exchanger between the common heat exchanger and the lower base of the frame.

A mixing device for distributing a mixture of a first phase and a second phase of a first fluid in a longitudinal direction in at least one passage of a heat exchanger, said mixing device including at least one lateral channel configured for the first phase to flow from at least one first inlet; a series of longitudinal channels extending in the longitudinal direction and each configured for the second phase to flow from a second inlet to a second outlet, said longitudinal channels succeeding each other in a lateral direction orthogonal to the longitudinal direction; and at least one opening fluidly connecting said lateral channel to at least one longitudinal channel such that the mixing device is configured to distribute a mixture of the first phase and the second phase via the second outlet of said longitudinal channel.

A method and system for controlling the nitrogen concentration in an LNG product and fuel from flash gas within preferred ranges. A cooled LNG stream is separated into a nitrogen-enriched vapor stream, a fuel stream, and an LNG product stream using a plurality of phase separating devices, such as flash drum or rectifying column. A portion of the vapor stream is recycled to the rectifying column as reflux. A portion of a stream having a higher concentration of nitrogen is combined with the fuel stream to maintain the fuel stream within a desired nitrogen concentration range.

A small to mid-scale liquefied natural gas production system and method is provided. The disclosed liquefied natural gas production system employs at least one heat exchanger, three turbine/expanders and at least three refrigerant compression stages. The expansion ratio of one turbine/expander is appreciably lower than the expansion ratio of the other turbine/expanders such that the temperature of the exhaust stream from the turbine/expander with the lower expansion ratio is above the critical point temperature of the compressed natural gas containing feed stream but colder than about −15° C. The present system and method may be configured using either a single nitrogen-based expansion refrigerant circuit or two separate refrigerant circuits wherein the turbine/expander with the lowest expansion ratio is contained within a separate refrigeration circuit from the other two turbine/expanders with the higher expansion ratios.

A system for processing liquified natural gas can include: a natural gas feed; a cold box; one or more natural gas cooling components; and a storage tank configured to store a refrigerant, wherein the one or more natural gas cooling components and the storage tank are located within the cold box. The cold box can be a methane cold box and the refrigerant can be propane, ethane, or ethylene. The system can also include a propane refrigerant cycle and/or an ethylene refrigerant cycle. Refrigerant stored in the methane cold box can be used to replenish refrigerant lost in the propane/ethylene cycles. The cold box can be an ethylene cold box of the ethylene refrigerant cycle. Propane can be stored in the ethylene cold box. A second storage tank can be located within a methane cold box and store ethane or ethylene.

A system and method for cooling, purifying and liquifying a feed gas stream uses liquid nitrogen for cooling the system. After cooling the system, the warmed nitrogen is vented as a vapor. The system and method include a water condenser, a first and second cooler and a liquifier and production of at least first and second contaminant streams. Optionally, the system includes a compressor or blower and/or a separator.