Volume 54

Preliminary study of a new CO2 resource utilization system that combines waste heat recovery and cold energy utilization Fulu Lu , Chuhan Pan , Hongguang Zhu , Qi Wu , Yanan Liao

Abstract

The bio-natural gas (BNG) industry, which utilizes organic waste to produce biogas and purify it into BNG, has gained rapid development because it is in line with global carbon neutrality targets and sustainable development strategies. However, the difficulty in utilizing the carbon dioxide separated by the purification system restricts the green development of the BNG industry. Liquid CO2 is easier to store and transport compared to gaseous state, but liquefaction not only consumes power but also requires a high-grade cold source. In this research, based on a BNG station with a daily production of 5000 m3, a novel CO2 resource utilization system is proposed, which combines the waste heat recovery of CO2 compression heat with the utilization of cold energy from liquid natural gas (LNG) gasification to achieve energy saving and consumption reduction. The system consists of a two-stage CO2 cascade compression system, an organic Rankine cycle system and an LNG gasification system. A thermodynamic analysis was conducted on the system, and the results show that the ORC system effectively recover the waste heat of the CO2 cascade compression system, reducing the power output by 12.8%. When the evaporation and condensation temperatures of the ORC system are 368.15 K and 303.15 K, respectively, the cold energy recovery rate of LNG gasification reaches 62.6%. The pressurization ratio of the CO2 cascade compression system and the evaporation temperature of the ORC system have a large impact on the combined system, and the exergy analysis and parameter optimization design will be carried out subsequently. This study will provide theoretical guidance for CO2 resource utilization in BNG industry.

Keywords CO2 resource utilization; Waste heat recovery; Cold energy utilization; System analysis