Design and optimization of CO₂ liquefaction purification and power generation process based on LNG cold energy

Objective In order to produce high purity CO₂ which can be directly used in industrial manufacturing and food processing, a new process using LNG cold energy for liquefaction and purification of CO₂ and power generation is proposed.

Method HYSYS software was used to simulate different cycle working fluids and different operating parameters. The influence of cycle working fluids on CO₂ liquefaction and Rankine cycle power generation was analyzed. The parameters of rectification column were optimized according to product energy consumption.

Result When the two-stage cycle working fluids were pure working fluids, the liquefaction amount and power generation of propylene + ethylene components were the largest, which were 377 900 kg/h and 2 284 kW, respectively. When the cycle working fluids were mixture, the liquefaction amount and power generation of the process were significantly higher than that of the pure working fluids. In the first cycle, the molar ratio of ethane and propylene of the mixing working fluids was 9∶1, and in the second cycle, the molar ratio of methane, ethylene and propylene of the mixing working fluids was 2.0∶6.0∶2.0, the liquefaction amount and power generation were the largest, which were 386 200 kg/h and 3 042 kW, respectively; the number of suitable rectification column plates was 30, the feeding position was the 10th tower plate, and the reflux ratio was 0.6.

Conclusion Compared with other processes such as single-stage Rankine cycle, the two-stage Rankine cycle process proposed in this paper has a higher CO₂ liquefacation rate and exergy efficiency, and can convert LNG cold energy into electric energy and produce high-purity liquid CO₂ products for cold energy utilization modules in LNG receiving stations.