Method and apparatus for obtaining liquid nitrogen by utilizing liquefied natural gas cold energy

Abstract

The invention relates to a method and a device for obtaining liquid nitrogen by utilization of the cooling capacity of liquefied natural gas. The method at least comprises the following steps: raw material nitrogen and the liquefied natural gas perform heat exchange in a natural gas heat exchanger; and the raw material nitrogen which is led out of an air separation unit or an external nitrogen pipe is compressed by a nitrogen turbocompressor, enters into a nitrogen channel of the natural gas heat exchanger for heat exchange, and is cooled by returned cold flow. The device consists of a low-temperature nitrogen circulator, the nitrogen turbocompressor, the natural gas heat exchanger, a high-temperature booster expansion turbine, a low-temperature booster expansion turbine, a gas-liquid separator and a liquid nitrogen subcooler. The method and the device fully utilize the high-quality cold energy of the liquefied natural gas, and can economically obtain liquid nitrogen; and the power consumption of the device in producing 1 kilogram of the liquid nitrogen is only 0.24 kilowatt per hour while the power consumption of the prior air separation unit in producing 1 kilogram of the liquid nitrogen is between 0.6 and 0.8 kilowatt per hour, so that the device has the characteristics of obvious energy-saving effect and so on.

Description

technical field [0001] The invention relates to a method and a device for recycling the cooling capacity of liquefied natural gas to obtain low-temperature liquid nitrogen, and belongs to the field of low-temperature technology. Background technique [0002] The main component of liquefied natural gas is methane, and a small amount of hydrocarbons such as ethylene and ethane. After deacidification and dehydration, the lowest temperature of liquefied natural gas is -162°C. Usually, LNG needs to be vaporized in seawater before being transported to land natural gas pipelines. During the vaporization process, LNG needs to release a large amount of cold (latent heat) when it is converted from a liquid state to a gaseous state. Under the pressure of 8MPa, the cooling capacity released when liquefied natural gas is vaporized from the liquid state -162C to the ambient temperature of 27°C is 830kJ / kg. If such a huge cooling capacity of liquefied natural gas is recovered, it can not ...

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Problems solved by technology

[0004] The purpose of the present invention is to overcome the disadvantage of consuming a large amount of electric energy to obtain liquid nitrogen by conventional methods, and to provide a method and device that can make full use of the cooling capacity of liquefied natural gas and recover the cooling capacity to obtain liquid nitrogen, and the method is easy to adapt to the current situation. Some systems are designed for the production of conventional liquid nitrogen

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