A Review of the Basics for Superior Design

摘要

From the thermodynamic point of view, cryogenic gas plants are open refrigeration cycles. A review of the concepts regarding the efficient use of energy leads us to the heart of the problem. Lost work, exergy analysis, and pinch technology, all revolve around the same concept of irreversibility, which results in thermodynamic lost work. Before the computer age, the use of these abstract concepts was left to the academic world. With today’s computer speed, the flexibility of process simulators and the link to pinch technology software, thermodynamic analysis of a process is much easier, and now plays a vital role in process design. In this paper we will show how calculations of ideal work, actual work, lost work, and overall process efficiency and equipment efficiencies help in the design of new process concepts or the comparison of options. The review will include estimates of lost work inside distillation columns, how it may be reduced, and how column targeting can be used for optimum heat integration of the process. When applied to a cryogenic gas plant, the analysis shows that the largest lost work is in recompression, which reemphasizes the need to run the column at as high of a pressure as possible. This is what led us to conceptualize the new High Pressure Absorber (HPA) process. A numerical and graphical comparison of different processes will be shown.