Liquefied natural gas (LNG) cold energy air separation system and air separation method

Abstract

The invention discloses a liquefied natural gas (LNG) cold energy air separation system and air separation method. The air separation system comprises an air separation unit, an LNG cold energy utilization unit and an ethylene glycol solution circulating and cooling unit. Through the new process organization form that a circulating liquid nitrogen pump is used for replacing a low-temperature circulating nitrogen compressor, production energy consumption of the LNG cold energy air separation system is substantially reduced, the extraction rate of oxygen and argon is high, the liquefaction ratioof a nitrogen product reaches up to 100%, and the additional value is high; moreover, a liquid nitrogen reverse current cold supplement mode is matched with LNG cold energy changes, and the LNG coldenergy air separation system has fewer requirements for an LNG receiving station and is high in universality. Compared with an existing LNG cold energy air separation technology, the LNG cold energy air separation system and air separation method have the beneficial effects that the comprehensive energy consumption is reduced by 40% or more, and the unit energy consumption is reduced by 60% or more; moreover, the unit energy consumption is still lower than that in the prior art under extreme production reduction conditions, and the cost advantages are quite obvious.

Description

technical field [0001] The invention relates to an air separation method, in particular to an air separation method utilizing the cold energy of liquefied natural gas. Background technique [0002] As one of the chemical energy sources, natural gas has been gradually promoted as the main energy pillar after coal and oil due to its huge reserves and low pollution, and has broad application prospects. The trade forms of natural gas mainly include pipeline transportation and LNG (liquefied natural gas) transportation. Before LNG enters the pipeline network of natural gas users, it needs to be gasified from a liquefied state to normal temperature. The gasification process will release a huge amount of cold energy. By making full use of the gasification cold energy of LNG, the air separation device can significantly reduce power consumption, increase liquid production, and improve the competitiveness of products in the market. The economic benefits are very obvious. However, sin...

AI Technical Summary

Problems solved by technology

Looking at LNG cold energy air separation plants at home and abroad, there are generally phenomena that the process organization is too complicated, and the energy consumption is high, the implementation is not easy, the operation control is inconvenient, or the safety and reliability are not good.

For example, multiple compressors, multiple expanders, separation tanks, etc. are used, and there are many heat exchanger channels, especially when LNG is high pressure, the heat exchanger channels are many, resulting in a sharp increase in cost

In addition, the process organization is complicated, and areas with many electrical components such as valves and measurement points need to be explosion-proof, which brings hidden dangers to the safety of the device.

[0003] Chinese patent application specification CN 101571340A discloses an air separation system that utilizes the cold energy of liquefied natural gas. The patent uses a three-stage low-temperature air intake cycle nitrogen compressor and an ethylene glycol cooling system, but the liquid oxygen product is mainly obtained by relying on The high-pressure subcooled liquid nitrogen in the low-pressure oxygen and LNG-nitrogen heat exchanger is throttled to the low pressure to exchange heat with it, and one of the cold sources of the supercooled circulating high-pressure liquid nitrogen is the throttled low-pressure liquid nitrogen, that is, circulating low-temperature nitrogen compression The inlet flow of a section of the machine is relatively large, resulting in high shaft power of the low-temperature nitrogen compressor

[0004] Chinese patent application specification CN 101532768A discloses an air separation system that efficiently utilizes the cold energy of liquefied natural gas. Some embodiments of the patent use a liquid expander instead of a throttle valve to expand high-pressure liquid nitrogen, but the cold energy transfer medium circulates nitrogen relying on low temperature Driven by a circulating nitrogen compressor, the circulating nitrogen is compressed to supercritical pressure, and the energy consumption is dozens of times higher than that of liquid nitrogen compressed by a liquid pump

And there is a large amount of high-purity nitrogen that is released due to inability to liquefy, resulting in a further increase in the comprehensive unit energy consumption of the system

Images