Abstract:

For the natural gas CO₂ removal project applied in the floating liquefied natural gas production storage and unloading system（FLNG），when the feed gas processing capacity and CO₂ content are both at a high level，the alkanolamine process has problems such as high energy consumption，large tower size，and tower performance being greatly affected by wind and wave shaking.In response to this issue，it was proposed to firstly use membrane separation technology for crude CO₂ removal from raw gas，and then use alkanolamine process for fine CO₂ removal from raw gas.Based on the production data of a certain deep⁃water gas field development project，a coupled process simulation model of "membrane separation+alkanolamine method" was established using HYSYS software.The model was compared and analyzed with the alkanolamine process in terms of equipment size，system energy consumption，hydrocarbons loss，etc.The results showed that the size of the tower（absorption tower and regeneration tower） in the "membrane separation+alkanolamine method" coupling process was smaller than that in the alkanolamine process.After the membrane separation process reducing the molar fraction of CO₂ in the feed gas from 28.8% to 15.0%~20.0%，the CO₂ concentration was then reduced to 98 mg/m³ using the membrane separation process，the total energy consumption of the system was decreased to 42%~61%，but the hydrocarbons loss rate was increased from 1.2% to 5.0%~8.0%，and the membrane area of the membrane separation equipment was 890~1 481 m³.The conclusion was that the coupling technology of "membrane separation+alkanolamine method" had potential in the field of FLNG natural gas CO₂ removal，and the process design should comprehensively consider system energy consumption，equipment investment，product revenue，and waste gas treatment.

Key words: membrane separation, alkanolamine method, carbon capture