Appropriate placement of compressors and expanders in sub-ambient processes

The conversion between heat and work is fundamental in engineering thermodynamics. While methodologies for the integration of heat have been well established since the 1970s, the integration of heat and work is much less discussed. One difficulty is that heat and work have different qualities and exergy is suggested used to quantify the combined effect. The problem is then to design a process including heat exchanger networks and pressure changing equipment such as compressors and expander so that exergy consumption is minimized (or exergy production is maximized). On the basis of a set of theorems developed, a systematic design methodology is presented in this paper. Minimum exergy consumption can be achieved following the design methodology. For the illustrative example, exergy consumption is reduced by 75.1% compared to the design where both compression and expansion starts at supply temperature. Copyright © 2016 Elsevier B.V. All rights reserved.