Liquefaction technology of CO₂-precooled dinitrogen expansion for large FLNG/FLPG device top module

In view of the key and difficult technology of FLNG/FLPG device which are different from conventional FPSO and onshore LNG plant, taking the deep water gasfield in South China sea as a research object, optimization analysis of liquefaction process scheme has been carried out for the device, offshore FLNG liquefaction process of CO₂-precooled dinitrogen expansion has been proposed with independent intellectual property. The key parameters affecting the performance of the process have been optimized, and the adaptability of the process to offshore FLNG device has been analyzed. The results show that when the two-stage refrigeration technology is used in the gas cooling process of the offshore FLNG device, the temperature in the first stage of CO₂ refrigeration is about -20 ℃, and -50 ℃ in the second stage, the outlet pressure of the nitrogen recycle compressor is set at 8 MPa, the division temperature of the two-stage nitrogen expansion refrigeration is set at -98 ℃, and the heat transfer temperature difference is about 8 ℃, then the total power consumption is 6.258×10⁴ kW, liquidation rate is 93.7%, and the specific power consumption is 0.327 1 kW·h/m³.This process is safe, simple, with compact equipment, economical and well adaptive to offshore working conditions.