Natural gas liquefying method for gas peak regulation and light hydrocarbon recovery

Abstract

This invention discloses a liquefying method for natural gas used in gas peak-tuning and light hydrocarbon recovery including the following steps: 1, pre-cooling 2, pre-separation, 3, expansion cooling, in which, the high-pressure natural gas got in step 2 is expanded in a turbine expander to middle pressure sphere to form a gas-liquid mixture by reducing the temperature of the fluid, the high-pressure natural gas liquid got in step 2 is enthalpy-expanded to the mid-pressure sphere via a restrictor to reduce the fluid temperature and form a gas-liquid mixture, 4, separation of gas and liquid: separating the mixture got in step 3 in a separator to obtain liquid and middle-pressure natural gas, in which, the liquid one is input into a storage tank for storing, the middle-pressure gas is taken as the cold source of pre-cooling in step 1 then enters into the middle-pressure natural gas pipe network.

Description

Technical field [0001] The invention relates to the technical field of natural gas liquefaction, in particular to a natural gas liquefaction method for gas peak shaving and light hydrocarbon recovery. Background technique [0002] With the continuous development of China's economy and the adjustment of energy structure, it is an inevitable development trend to use clean energy and vigorously develop the natural gas industry. Before 2020, my country will invest 220 billion yuan in natural gas infrastructure construction: laying 50,000 kilometers of natural gas pipelines; setting up about 10 liquefied natural gas (LNG) stations in the Yangtze River Delta, Bohai Rim and Pan-Pearl River regions, Construct LNG receiving facilities with an import scale of 50 million tons; form a million-ton LNG transportation capacity. As a high-quality clean energy, natural gas also contains a large amount of light hydrocarbon resources, which are very good chemical raw materials. The recovery of ligh...

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Problems solved by technology

[0010] 1. U.S. Patent US6449982, but it needs to use an external cold source to liquefy all the raw material gas, and the operating cost of the process is relatively high

[0011] 2. U.S. patents US6023942 and US6209350, but the process is more complicated, and many compressors are used, which makes the investment and power consumption very large, so it is not suitable for use in the pressure regulating station of the natural gas transmission and distribution pipeline

[0012] 3. U.S. patents US6085546 and US6269656 only use the cooling capacity obtained by expansion to condense the feed gas, but do not separate the LNG produced during the expansion process of the feed gas in the turbo expander, which reduces the liquefaction rate of the process

[0013] 4. U.S. patents US6085547 and US6743829 use throttle valve expansion refrigeration. Since the refrigeration effect of isenthalpy throttling expansion is lower than the isentropic expansion of turbo expander, the cooling capacity obtained is less, which affects the liquefaction rate of the process

[0014] 5. The heat exchange network of the US patent US6378330 is not highly integrated, and the cooling capacity of low-temperature natural gas generated during the production of LNG is not utilized

[0015] 6. In the Chinese patent 200410085540.0 (application number), the pressure of natural gas can be used to do work externally to obtain the cooling capacity required for natural gas liquefaction, but this patent needs to use the method of refrigerant circulation to pre-cool the raw gas, so the energy consumption and operating costs are low. higher

[0016] 7. Chinese patent 02827305.2 (application number) is also a process for producing LNG through expansion refrigeration, but the process is relatively complicated. The LNG produced in the expansion process of the turbo expander is not separated, and only a part of the pre-cooled raw material is used Gas throttling, thereby reducing the natural gas liquefaction rate of the process

[0017] 8. The natural gas liquefaction device researched by the Cryogenic Center of the Chinese Academy of Sciences (Gu Anzhong, On the Development of the LNG Industry, P&cc's CHINALNG——"Petrochemical Construction" LNG Construction Special Issue, 2005) can be used in the pressure regulating station of the natural gas pipeline network. like figure 1 shown, but this process still has the following deficiencies: (1) The heavy hydrocarbons separated from the gas-liquid separator are not depressurized, so the pressure is very high, which is not conducive to storage and transportation; at the same time, the cold energy of heavy hydrocarbons is not fully utilized, Therefore, the utilization rate of cold energy is low

(2) Natural gas expands through the expander to generate low temperature, and part of the natural gas will be liquefied, and the gas-liquid mixture enters the heat exchanger 2 together as a refrigerant, without separating the LNG, which reduces the liquefaction rate of the process

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