The present invention relates to a method of controlling the production of a liquefied natural gas product stream (31) obtained by removing heat from natural gas by indirect heat exchange with an expanded heavy mixed refrigerant and an expanded light mixed refrigerant. The method comprises executing a control loop comprising maintaining the flow rate of the liquefied natural gas product stream (31) at a dependent set point and maintaining the flow rates of the heavy mixed refrigerant (60a) and the light mixed refrigerant (65) at operator manipulated set points (80, 81). The method further comprises executing an override control loop comprising: determining an override set point (95′) for the flow rate of the liquefied natural gas and computing an override set point (80′) for the flow rate of the heavy mixed refrigerant and an override set point (81′) to reduce residual available power of the electric motor.

A liquefaction apparatus that automatically adjusts the load on the liquefaction apparatus correspondingly with an upper limit value of contracted power in different time slots, and which is capable of maximizing the amount of liquefied product produced and of achieving optimum operating efficiency is provided. In certain embodiments, the liquefaction apparatus can include: a production amount calculation unit 91 for obtaining an actual production amount of a liquefied product; a predicted power calculation unit 92 for obtaining a predicted power amount after a predetermined time has elapsed, on the basis of an integrated power value obtained by integrating a usage power; and a power demand control unit 93 for comparing the predicted power amount and a moving average of instantaneous power, and controlling a discharge flow rate of a compressor 3 in such a way as to come infinitely close to a target value, without exceeding the target value, and while using the larger value of the predicted power amount and the moving average of instantaneous power as a value being controlled.

Disclosed techniques include controlled liquefaction and energy management. A gas within a first pressure containment vessel is pressurized using a column of liquid. The gas that is being pressurized is cooled using a liquid spray, wherein the liquid spray is introduced into the first pressure containment vessel in a region occupied by the gas. The liquid spray keeps the pressurizing to be isothermal. The gas that was pressurized is metered into a second pressure containment vessel, wherein the metering enables liquefaction of the gas. The gas that was pressurized is stored in a gas capacitor prior to the metering. The gas that was liquefied in the second pressure containment vessel is pushed into a holding tank, wherein the holding tank stores a liquefied state of the gas, and wherein the pushing is accomplished by the pressure of the gas that was metered into the second pressure containment vessel.

A method for controlling the refrigerant composition in a pre-cooled mixed refrigerant (PMR) cycle for LNG production includes obtaining a weather forecast temperature, measuring the concentration of each PMR component and measuring the ambient temperature. The method further includes calculating the optimum concentration of each PMR component for each of the measured and weather forecast temperatures and calculating the time period required to change appropriately each component concentration in transition from the ambient temperature to the weather forecast temperature; and comparing the measured and optimum concentration of each component in view of the calculated time period and direction of change in the component concentrations during the time period.

A method for enhancing a LNG production train that includes connected train components. The method may include steps of: constructing an integrated surveillance system for monitoring operation of the train components; using the integrated surveillance system to measure and record operational data and event data related to, respectively, the operation and a failure event of the train components over a historical operating period; performing a correlation analysis that calculates a correlation between the occurrences of the failure event and the operational data; given results of the correlation analysis, deriving a prognostic rule that indicates a likelihood of the failure event occurring based on values of the operating parameters of the operational data; applying the prognostic rule to current values of the operating parameters and determining therefrom the likelihood of the failure event occurring; determining an advisory related to the determined likelihood of the failure event occurring; and issuing the advisory.

Systems and methods are provided for adjusting a composition, pressure, and/or flow rate of a mixed refrigerant (MR) fluid in a liquefaction system to provide refrigeration to natural gas (NG) feedstock to produce liquefied natural gas (LNG). The MR fluid that is in circulation within a liquefaction system can include heavy components and light components. During LNG production, heavy components and/or light components of the MR fluid can be selectively removed from, and reintroduce into the MR fluid, thereby altering the composition of the remaining MR fluid in circulation. Adjusting the composition of the MR fluid in circulation within a liquefaction system can allow the system to be optimized to maximize efficiency, LNG production, and or profitability while the system is in operation.

A liquefied gas cooling apparatus including: a gas flow path for carrying a liquefied gas that is liquefied by cooling; and a refrigeration unit including a refrigerating cycle formed by an evaporator for cooling the liquefied gas flowing through the gas flow path, a compressor, a condenser, and a throttle expansion unit. The compressor is driven through an electric motor contained in a sealed housing together with a compressor mechanism.

A method for operating a main cryogenic heat exchanger for use in a natural gas liquefaction process, involves monitoring or predicting variations in the flow rate of a feed gas stream provided to the main cryogenic heat exchanger. When a variation of the flow rate exceeding a predetermined threshold value is monitored or predicted, a control scheme is started to control one or more compressor recycle valves in response to the monitored or predicted variation of the flow rate to recycle part of a compressed mixed refrigerant stream in a refrigerant loop.

The invention relates to compression refrigerator control systems, viz. to refrigerant composition control in premixed refrigerant cycle of liquefied natural gas (LNG) production. The method for controlling the refrigerant composition in the pre-cooled mixed refrigerant (PMR) cycle for LNG production comprises controlling in view of the weather forecast temperatures. The method comprises measuring the concentration of each PMR component and measuring the ambient temperature. Further, it comprises calculating the required concentration of each component for each of the measured and weather forecast temperatures on the basis of the predetermined relationship between the optimum concentration of each component and ambient temperature; calculating the time period required to change appropriately each component concentration in transition to the following of the weather forecast temperatures by using the highest possible change (increase or decrease) rate of each component concentration for the said cycle; and comparing the measured and required concentration of each component in view of the calculated time periods and direction of change in the component concentrations during these periods. The invention allows a higher efficiency of the pre-cooling cycle due to maintaining the optimum PMR composition thus minimizing the cooled product temperature in LNG production.

A liquefaction apparatus that automatically adjusts the load on the liquefaction apparatus correspondingly with an upper limit value of contracted power in different time slots, and which is capable of maximizing the amount of liquefied product produced and of achieving optimum operating efficiency is provided. In certain embodiments, the liquefaction apparatus can include: a production amount calculation unit 91 for obtaining an actual production amount of a liquefied product; a predicted power calculation unit 92 for obtaining a predicted power amount after a predetermined time has elapsed, on the basis of an integrated power value obtained by integrating a usage power; and a power demand control unit 93 for comparing the predicted power amount and a moving average of instantaneous power, and controlling a discharge flow rate of a compressor 3 in such a way as to come infinitely close to a target value, without exceeding the target value, and while using the larger value of the predicted power amount and the moving average of instantaneous power as a value being controlled.