System And Method For Natural Gas Liquefaction

Abstract

The present invention provides an LNG production system and method with improved refrigeration. The refrigeration is achieved by a refrigeration device comprising a plurality of refrigerant compressors (11, 13, 15, 17) configured into a series arrangement to perform multi-stage compressions of a refrigerant, a plurality of aftercoolers (12, 14, 16, 18) each of which being coupled to each of the plurality of refrigerant compressors to cool the compressed refrigerant, a plurality of turboexpanders (19, 20) coupled to the last aftercooler (18) and configured into a series configuration to perform multi-stage expansions of the compressed refrigerant, and a plurality of refrigerant heat exchange means (33, 34) coupled to both the first (11) of the plurality of refrigerant compressors and the last (20) of the plurality of turboexpanders, so that all components form a close refrigeration cycle.

Description

FIELD OF THE INVENTION[0001]The present invention relates generally to the technology of natural gas liquefaction, and more particularly to a system and method for natural gas liquefaction employing a plurality of turboexpanders configured into a series arrangement.BACKGROUND OF THE INVENTION[0002]To transport the natural gas in a more efficient way, it is important to liquefy it into liquefied natural gas (LNG) for transportation, which enables to shrink the volume of the natural gas by 600 times so it can be shipped to customers in other parts of the world. Many LNG liquefaction plants utilize a refrigeration cycle with mixed refrigerants where cooling is generally achieved by heat exchange using refrigerant with one or more compositions including propane, propylene, ethane, ethylene, methane and nitrogen or mixtures thereof, in a closed loop or open loop configuration. Mixed refrigerant cycles are efficient as they can closely approach the cooling curve of the natural gas and mul...

AI Technical Summary

Benefits of technology

[0007]One objective of this invention is to provide an LNG production system with improved refrigeration efficiency.

[0010]In another embodiment of the LNG production system, the natural gas liquefaction subsystem comprises a gas treatment module for treating the pressurized natural gas so as to make it suitable for being liquefied, a natural gas heat exchange means fluidly / gaseously coupled with the gas treatment module and disposed within the main cryogenic heat exchanger for enabling the passing-through pressurized natural gas to exchange heat with countercurrent refrigerant flows, and a natural gas pressure reduction means fluidly / liquidusly coupled with the natural gas heat exchange means for controlling the reduction of the pressures of the pressurized liquefied natural gas from the natural gas heat exchange means so as to further reduce the temperature of the pressurized liquefied natural gas, yielding LNG and flash gas.

Problems solved by technology

However, the performance of LNG process is limited by several factors, such as the maximum temperature approach limitation of the main cryogenic heat exchanger, and the limited expansion ratio achieved by a single expander.

However, the refrigerant mass flow rate in these processes is high.

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