Dual-refrigerant liquefaction system and method for NG (Natural Gas)

Abstract

The invention relates to a dual-refrigerant liquefaction system and a dual-refrigerant liquefaction method for NG (Natural Gas). The system comprises a cold box for liquefying the NG, an NG supply pipe, a No.1 refrigerant external treatment subsystem, a No.2 refrigerant external treatment subsystem, a No.1 refrigerant cooling subsystem, a No.2 refrigerant cooling subsystem, a heavy hydrocarbon separation tank which is used for realizing gas-liquid separation of heavy hydrocarbon and light hydrocarbon, and a denitrification tank, wherein the cold box comprises an NG precooling passage which is used for cooling liquid heavy hydrocarbon components and gas light hydrocarbon components obtained through cooling; an NG deep cooling passage which is used for liquefying the gas light hydrocarbon components; a No.1 refrigerant precooling passage which is used for cooling high-pressure normal-temperature No.1 refrigerant; a No.2 refrigerant first section precooling passage and a No.2 refrigerant second section precooling passage which are used for cooling No.2 refrigerant; a No.1 refrigerant cooling passage which is used for cooling the NG, the high-pressure normal-temperature No.1 refrigerant and high-pressure normal-temperature No.2 refrigerant by using low-pressure low-temperature No.1 refrigerant; and a No.2 refrigerant cooling passage which is used for cooling the light hydrocarbon components and the No.2 refrigerant by using low-pressure low-temperature No.2 refrigerant. By adopting the technical scheme, the complexity and the energy consumption of the system can be reduced.

Description

technical field [0001] The invention relates to a natural gas double refrigerant liquefaction system and a liquefaction method. Background technique [0002] Natural gas (NG) is a gaseous substance under ambient conditions, and it is very uneconomical to transport it to users through pipelines over long distances, especially when it is necessary to cross the ocean or cannot lay pipelines. Therefore, to realize the transportation and utilization of natural gas , which must be liquefied into liquefied natural gas (LNG). [0003] The industrial application of natural gas liquefaction technology began in the 1960s. Since its development, the mature natural gas liquefaction process can be divided into three types, namely cascade refrigeration process, expansion refrigeration process and mixed refrigerant refrigeration process. Among them, cascade refrigeration process The circulation process of the process has many units, complicated control, and inconvenient maintenance, so it ...

AI Technical Summary

Problems solved by technology

[0006] visible, image 3 The existing mixed refrigerant liquefaction system shown in the figure liquefies NG. At least two cold boxes are required to meet the requirements. The two refrigerants in this technology work independently and are cooled independently, so the complexity of the entire liquefaction system and higher energy consumption

In addition, when the No. 1 refrigerant uses propane, its physical characteristics determine that the lowest temperature it can achieve for NG precooling is a fixed value of about -40°C. Therefore, when the composition of NG changes, or at ambient temperature When changing with the seasons, the LNG output of the liquefaction system will be unstable, especially when the ambient temperature is below -40°C, the liquefaction of NG does not require propane pre-cooling, but if the No. 1 heat exchanger 201 is not used , the whole liquefaction system will not work, so the energy consumption of the liquefaction system is quite large

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