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.

Described is a process for production of Liquefied Natural Gas (LNG) that optimises an offset turbo expansion chilling curve attributed to the refrigerant properties inherent to the natural gas feedstock for the majority of chilling, followed by a smaller externally sourced heat exchange to make the final phase transition to LNG. This process reduces the complexity and high capital costs associated with traditional LNG systems.

A refrigerant cycle pressure control system includes: a heat exchanger cooling boil-off gas received from a storage tank; a refrigerant cycle including a refrigerant circulation line, a refrigerant compressor, and an expander; an inventory tank storing the refrigerant to be charged to the refrigerant cycle; a refrigerant supply line connecting the inventory tank to an upstream side of the refrigerant compressor to replenish the refrigerant cycle with the refrigerant; a refrigerant discharge line connecting a downstream side of the refrigerant compressor to the inventory tank to discharge the refrigerant from the refrigerant cycle to the inventory tank; and a pressure regulation line branched off of the refrigerant discharge line. The refrigerant cycle is depressurized by discharging the refrigerant from the refrigerant cycle through the refrigerant discharge line or the pressure regulation line.

A method and apparatus for liquefying a feed gas stream comprising natural gas and carbon dioxide. A method includes compressing an input fluid stream to generate a first intermediary fluid stream; cooling the first intermediary fluid stream with a first heat exchanger to generate a second intermediary fluid stream, wherein a temperature of the second intermediary fluid stream is higher than a carbon dioxide-freezing temperature for the second intermediary fluid stream; expanding the second intermediary fluid stream to generate a third intermediary fluid stream, wherein the third intermediary fluid stream comprises solid carbon dioxide; separating the third intermediary fluid stream into a fourth intermediary fluid stream and an output fluid stream, wherein the output fluid stream comprises a liquefied natural gas (LNG) liquid; and utilizing the fourth intermediary fluid stream as a cooling fluid stream for the first heat exchanger.

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.

A liquefaction system comprises: a temperature setting unit for setting an inlet gas temperature on entry to a cold turbine; a control valve for controlling an amount of gas fed to the cold turbine, correspondingly with an inlet gas temperature measured by the temperature measuring unit; and a control unit which compares the inlet gas temperature measured by the temperature measuring unit with a warning temperature set value plus a margin, and sets a first operating state when the inlet gas temperature is equal to or less than the warning temperature set value plus the margin and also sets an emergency stoppage temperature set value at the warning temperature set value plus the margin, and sets a second operating state when the inlet gas temperature is greater than the warning temperature set value plus the margin, the control unit performing control in response to the second operating state to make a degree of opening of the control valve greater than a degree of opening during the first operating state in order to lower an inlet pressure of the cold turbine, and performing control in response to the first operating state to make the degree of opening of the control valve smaller than the degree of opening during the second operating state in order to raise the inlet pressure of the cold turbine.

A method and apparatus for producing liquefied natural gas. A pretreated natural gas stream is compressed in at least two serially arranged compressors to a pressure of at least 1,500 psia and cooled. The resultant cooled compressed natural gas stream is expanded in at least one work producing natural gas expander to a pressure less than 2,000 psia and no greater than the pressure to which natural gas stream has been compressed, thereby forming a chilled natural gas stream that is separated into a refrigerant stream and a non-refrigerant stream. The refrigerant stream is warmed in a heat exchanger through heat exchange with one or more process streams associated with pretreating the natural gas stream, thereby generating a warmed refrigerant stream. The warmed refrigerant stream and the non-refrigerant stream are then liquefied.

A system and method for producing liquefied natural gas are provided. The method may include compressing a process stream containing natural gas in a compression assembly to produce a compressed process stream. The method may also include removing non-hydrocarbons from the compressed process stream in a separator, and cooling the compressed process stream with a cooling assembly to thereby produce a cooled, compressed process stream containing natural gas in a supercritical state. The method may further include expanding a first portion and a second portion of the natural gas from the cooled, compressed process stream in a first expansion element and a second expansion element to generate a first refrigeration stream and a second refrigeration stream, respectively. The method may further include cooling the natural gas in the cooled, compressed process stream to a supercritical state with the first and second refrigeration streams to thereby produce the liquefied natural gas.

Disclosed herein is a BOG reliquefaction method for LNG ships. The BOG reliquefaction method for LNG ships includes: 1) compressing BOG; 2) cooling the BOG compressed in Step 1) through heat exchange between the compressed BOG and a refrigerant using a heat exchanger; 3) expanding the BOG cooled in Step 2); and 4) stably maintaining reliquefaction performance regardless of change in flow rate of the BOG compressed in Step 1) and supplied to the heat exchanger to be used as a reliquefaction target.

Disclosed is a device for refrigerating or liquefying a fluid such as natural gas or hydrogen, comprising a fluid circuit that is to be cooled and has an upstream end for connection to a source of gaseous fluid as well as a downstream end for connection to a member for collecting the cooled or liquefied fluid, the device comprising a heat exchanger assembly in heat exchange with the fluid circuit to be cooled, the device comprising a refrigerator in heat exchange with at least a portion of the exchanger assembly, the refrigerator being of the type that has a cycle for refrigerating a cycle gas containing at least one of: helium, hydrogen, nitrogen or neon; said refrigerator comprising in series in a cycle circuit: a mechanism for compressing the cycle gas, at least one member for cooling the cycle gas, a mechanism for expanding the cycle gas, and at least one member for reheating the expanded cycle gas, wherein the compression mechanism comprises a plurality of compression stages in series composed of a centrifugal compressor assembly, the compression stages being mounted on a set of shafts that are rotationally driven by a motor assembly, the at least one member for cooling the cycle gas comprising at least one heat exchanger at the outlet of at least one compression stage in heat exchange with the cycle circuit, said heat exchanger being cooled by a heat transfer fluid, characterized in that the compression mechanism comprises at least two compression stages that are arranged successively in series and do not include any member for cooling the cycle gas such as a heat exchanger therebetween.