A Novel Nitrogen Pipeline System for Recycling Pressure Energy: System Model and Energy Efficiency Economic Analysis

The depressurization process by throttling causes a large amount of pressure energy loss in the nitrogen delivery process. We propose a novel nitrogen piping system (NNPS) and determine the key technical parameters to recover the pressure energy. The NNPS recovers nitrogen pressure energy for power generation and uses post-expansion cold energy to further reduce feedstock nitrogen temperature and compression energy consumption. We selected an NPS in China as a case study to analyze the performance of the NNPS under various operating conditions through energy, exergy, and economic analysis. In addition, a sensitivity analysis of the pre-expansion pressure was carried out. Results show that when the two throttling processes are replaced by the expansion process, the power generation per unit mass flow rate is 77.37 kW, and the energy consumption per unit mass flow rate of the compressor is reduced by 24.49 kW. Moreover, the energy efficiency and the exergy efficiency are 18.67 % and 16.86 % higher in NNPS compared with those in the NPS, respectively, with the shortest payback period of 113.2 days. When the expansion outlet pressure is 1.6 MPa, the system is suitable for construction when the pre-expansion pressure is higher than 2.0 MPa.