Method and system for manufacturing compressed natural gas through low concentration gas

Abstract

The invention discloses a method for manufacturing compressed natural gas through low concentration gas. The method includes the steps that after the low concentration gas enters a compressor 1 to be compressed, the low concentration gas enters a PSA device I for concentrating, absorption exhaust gas of the PSA device I and absorption exhaust gas of a PSA device III enter a PSA device II to recycle nitrogen, the nitrogen returns to an inlet of the compressor 1, methane mixed gas concentrated by the PSA device I is pressurized and then enters the PSA device III for concentrating, one part of the methane mixed gas behind the PSA device III is deoxidized to manufacture product gas, the other part of the methane mixed gas serves as displacement gas to enter the PSA device I and the PSA device III respectively or to enter the PSA device III first and then enter the PSA device I, displacement exhaust gas enters the inlet of the compressor 1, and flue gas of the PSA device I and flue gas of the PSA device III enter respective regenerated towers respectively to recycle nitrogen. The invention further discloses a corresponding system for manufacturing the compressed natural gas through the low concentration gas. The method enables the oxygen content to be always kept smaller than the oxygen content allowed by explosion in the absorption process, and is safe, low in power consumption and high in recycling rate.

Description

technical field [0001] The invention relates to a technology for enriching low-concentration gas, in particular to a method and system for producing compressed natural gas by utilizing low-concentration gas. Background technique [0002] With the development of urbanization, the annual growth rate of my country's natural gas consumption has remained above 10%. In 2013, my country's conventional natural gas output was 114.7 billion cubic meters, and the apparent consumption reached 167.6 billion cubic meters. The import volume increased by 25% year-on-year, reaching 53 billion cubic meters, the annual dependence on foreign natural gas reached 31.6%. It is estimated that my country's natural gas consumption will increase to 300 billion cubic meters in 2020, and about 50% will depend on imports by then. On the other hand, my country's coalbed methane resources have reached 36.8 trillion cubic meters, which is equivalent to conventional natural gas reserves and can be used as an...

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Problems solved by technology

[0003] In my country, the gas emitted into the atmosphere due to coal mining is more than 30 billion cubic meters per year, and the utilization rate is less than 10%, resulting in serious waste of resources and environmental pollution.

[0009] However, according to the above-mentioned invention application, it is found that when the methane concentration in the raw gas is very low (for example, the gas concentration is 15%), in order to reduce the oxygen content entering the pressure swing adsorption, the amount of nitrogen added is generally required to reach more than 75% of the raw gas amount , while the original nitrogen concentration in the raw material gas itself is lower than 70%, and pressure swing adsorption nitrogen production has a certain yield. At this time, it is necessary to increase air separation nitrogen production, thereby increasing investment and energy consumption, and reducing economic benefits

On the other hand, after adding a large amount of nitrogen, the concentration of methane in the mixed gas of PSA is lower than 10%, while the concentration of nitrogen is higher than 80%. The separation coefficient of methane and nitrogen on each adsorbent is low, in order to improve the product The concentration of methane, the process setting will be more complicated, which will increase the energy consumption

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