Thermodynamic Analysis on Work Transfer Process of Two Gas Streams

• Published in: Industrial & engineering chemistry research Vol. 49; no. 24; pp. 12496 - 12502
• Main Authors: Deng, Jian-Qiang, Shi, Ji-Quan, Zhang, Zao-Xiao, Feng, Xiao
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 15.12.2010
• Subjects: Applied sciences; Chemical engineering; Exact sciences and technology; Process Design and Control; Thermodynamic analysis
• ISSN: 0888-5885; 1520-5045
• DOI: 10.1021/ie1011323

A novel concept of gas−gas work exchanger (WE) is proposed for recovery of mechanical energy. Its thermodynamic process is analyzed by using the energy conservation law and the real gas’s pressure-specific enthalpy diagram. An in-depth work evaluation model of the work transfer process is carried out. A simplified equation for quick forecast work recovery efficiency of a gas-gas work exchanger is derived. The performances of a gas−gas work exchanger are analyzed by predigesting some precondition. The work recovery efficiency of a gas−gas work exchanger is found to be lower than that of a liquid−liquid work exchanger, e.g., the work recovery efficiency of a diatomic molecule gas drops from 0.75 to 0.46 as the compression ratio is increased from 1.5 to 3.0. The higher compression rate results in more work loss. In the example case of this work, supposing the same nitrogen stream supplies the power for recovery, a three-stage recovery process can recover 79% more power than a single stage process. A low-pressure stream can be compressed and rise its temperature far higher than that of two original temperatures of the streams. It is a new approach to energy transfer driven by pressure difference and it is wholly different from the heat transfer in a heat exchanger (HE). A network combining WEs with HEs is proposed for recovering energy thoroughly and flexibly.