Exergy analysis of large-scale helium liquefiers: Evaluating design trade-offs

Abstract

Abstract. It is known that higher heat exchanger area, more number of expanders with higher efficiency and more involved configuration with multi-pressure compression system increase the plant efficiency of a helium liquefier. However, they involve higher capital investment and larger size. Using simulation software Aspen Hysys v 7.0 and exergy analysis as the tool of analysis, authors have attempted to identify various trade-offs while selecting the number of stages, the pressure levels in compressor, the cold-end configuration, the heat exchanger surface area, the maximum allowable pressure drop in heat exchangers, the efficiency of expanders, the parallel/series connection of expanders etc. Use of more efficient cold ends reduces the number of refrigeration stages and the size of the plant. For achieving reliability along with performance, a configuration with a combination of expander and Joule-Thomson valve is found to be a better choice for cold end. Use of multi-pressure system is relevant only when the number of refrigeration stages is more than 5. Arrangement of expanders in series reduces the number of expanders as well as the heat exchanger size with slight expense of plant efficiency. Superior heat exchanger (having less pressure drop per unit heat transfer area) results in only 5% increase of plant performance even when it has 100% higher heat exchanger surface area.

Optimum Expanded Fraction for an Industrial, Collins-Based Nitrogen Liquefaction Cycle

“…The cycle does not correspond to the standard cycle of Figure 1 . As any industrial cycle, it must be adapted to the requirements of the product and integrate modifications for large-scale liquefaction [ 15 ]. The high pressure level of the cycle is 36 bar, close to the critical 33.9 bar, so in contrast to the helium case, the large variations in specific heat mentioned earlier will affect the last stage of the heat exchange and appear clearly on the temperature profiles.…”